2.) Follow the lingual a. from its origin, the external carotid a., to where it dives deep to the hyoglossus m.

Note: The lingual a. is an anterior branch of the external carotid a. (ECA) and often shares a common trunk with the facial a. If not, it commonly branches from the ECA proximal to the facial a. It can be seen in this area passing deep to the hyoglossus m. to supply the majority of the floor of the mouth and tongue. This artery will be dissected in more detail shortly.

Photo 2. Lingual a.

Examine the oral cavity proper - SUPERFICIAL SIDE

Find these structures:

• Oral cavity proper

• Oral vestibule

• Gingiva

• Teeth

  • Incisors (central & lateral)

  • Canines

  • Premolars (first & second)

  • Molars (first, second, & third)

3.) Identify the oral cavity proper, oral vestibule, gingiva, and the different types of teeth.

Note: The oral cavity can be divided into the oral cavity proper and the oral vestibule. The occlusal plane of the teeth divides these areas: oral cavity proper is internal to teeth, and the oral vestibule is external.

Note: The gingivae are masticatory mucosae that cover the roots of teeth and portions of the alveolar processes of the maxilla and mandible. It appears light pink and is closer to the teeth than the darker pink alveolar mucosa.

Note: There are four types of adult teeth: incisors (8), canines (4), premolars (8), and molars (12). The actual numbers of these types may vary among individuals.

Photo 3. Oral vestibule, teeth and gingiva, & oral cavity proper

Investigate the tongue, structures of the tongue, and associated structures of the tongue - DEEP SIDE

Find these structures:

• Tongue & Associated Structures

  • External tongue

    • Body (presulcal part)

    • Root (postsulcal part)

    • Median sulcus (of tongue)

    • Filiform papillae

    • Fungiform papillae

    • Vallate papillae

    • Terminal sulcus (of tongue)

    • Foramen caecum (of tongue)

  • Lingual tonsil

  • Suprahyoid mm.

    • Digastric m., anterior belly

    • Mylohyoid m.

    • Geniohyoid m.

  • Extrinsic tongue mm.

    • Hyoglossus

    • Styloglossus

    • Genioglossus

  • Intrinsic tongue mm.

    • Superior longitudinal m.

    • Inferior longitudinal m.

    • Transverse m.

    • Vertical m.

  • Associated Structures

    • Lingual frenulum (frenulum of tongue)

    • Sublingual fold

      • Openings of sublingual ducts

    • Sublingual caruncle

    • Fimbriated folds

    • Epiglottis

    • Epiglottic valleculae

    • Median glosso-epiglottic fold

    • Lateral glosso-epiglottic folds

4.) Turn the hemisected head so that a medial view of the tongue is possible. Identify the extrinsic and intrinsic tongue mm and associated muscles.

Note: When observing a medial view of the bisected tongue, the muscles are organized from inferior to superior: suprahyoid mm. (anterior belly of digastric m., mylohyoid m., geniohyoid m.), and tongue mm. (genioglossus m., and intrinsic muscles of the tongue).  

Note: The mylohyoid m. forms the bulk of the floor of the oral cavity and can be identified superior to the digastric m. Like the anterior belly of digastric m., it is innervated by the nerve to mylohyoid (a branch of inferior alveolar n.,V3). When contracted, the mylohyoid m. elevates the tongue and hyoid, and can also depress the mandible.

Note: Geniohyoid m. attaches the mandible (inferior mental/genial spine) to the hyoid; thus, when it contracts, it will elevate the hyoid bone. When the hyoid is fixed, geniohyoid m. can play a role in depression of the mandible. Recall that geniohyoid is not a tongue muscle, and is innervated by branches from the VPR of C1 that travel with the hypoglossal n. (CN XII).

Note: Genioglossus m. is the most expansive extrinsic tongue muscle, and in sagittal section appears roughly triangular in shape. Its attachment to the mandible is on the superior mental/genial spines; thus, it is located superior to the geniohyoid m. These muscles when contracting bilaterally will depress and protrude the tongue. Acting unilaterally, genioglossus m. will deviate to the contralateral side.

Note: There are four types of intrinsic muscles of the tongue: superior longitudinal, inferior longitudinal, transverse, and vertical. These muscles independently (and in unison) alter tongue shape and perform smaller, more precise movements.

Photo 4. Medial view of tongue

5.) Using blunt dissection (scissors), carefully remove the oral mucosa superior to the sublingual space. A safe place to incise the mucosa is along the mucogingival junction adjacent to the mandible. Also using blunt dissection, remove the mental spine attachments of the geniohyoid m. and genioglossus m., and reflect the tongue posteromedially to open the sublingual space.

Photo 5. Procedural: removing mucosa

6.) Locate the remaining extrinsic tongue muscles: styloglossus m. and hyoglossus m.

Note: Styloglossus m. attaches the styloid process of the temporal with the posterolateral tongue. Innervated by the hypoglossal n. (CN XII), the styloglossus m. retracts and elevates the tongue.

Note: Hyoglossus m. attaches the greater horn of the hyoid bone to the intrinsic muscles of the tongue. Innervated by the hypoglossal n. (CN XII), the hyoglossus m. retracts the tongue and depresses the ipsilateral side of the tongue.

Photo 6. Hyoglossus m. and styloglossus m.

7.) Locate the following tongue structures from a superior view of the dorsum of the tongue: medial lingual sulcus, filiform papillae, fungiform papillae, vallate papillae, sulcus terminalis, foramen caecum, and lingual tonsil.

Note: The lingual papillae consist of four types (from anterior to posterior): filiform, fungiform, foliate, and vallate. All lingual papillae are associated with taste buds, except filiform.

Note: Filiform papillae are small, conical eruptions covering the dorsal anterior two-thirds of the tongue.

Note: Fungiform papillae are moderately sized, mushroom-shaped eruptions interspersed throughout the filiform papillae. Fungiform papillae host taste buds innervated by the axons from chorda tympani (facial n.) by way of the lingual n. (V3).

Note: Vallate papillae (sometimes referred to as circumvallate papillae) are located on the posteriormost border of the oral part of the dorsal tongue, just anterior to the terminal sulcus and foramen caecum. These papillae are the largest of the lingual papillae. Vallate papillae host taste buds innervated by the axons from the glossopharyngeal n. (CN IX), even though they lie on the presulcal side of the tongue.

Photo 7. Dorsum of tongue

Note: The median sulcus runs from the tip of the tongue to the foramen caecum, and divides the dorsum of the tongue into two halves. Deep to the median sulcus is a fibrous septum, which divides the length of the tongue.

Note: Foramen caecum is an indention located in the midline of the terminal sulcus of the tongue. This is an embryonic remnant of the thyroid diverticulum and thyroglossal duct.

The terminal sulcus is the midline junction of the body and root of the tongue.

Note: Paired terminal sulci run from the foramen caecum anterolaterally to the palatoglossal arch to form a V-shape. The terminal sulci divide the dorsum of the tongue into the body (presulcal) and root (postsulcal). The terminal sulci run parallel to the vallate papillae.  

Note: The lingual tonsil is located on the root of the tongue. This tonsil is composed of groups of lymphoid follicles covered with mucosa.

Photo 8. Dorsum of tongue

Note: The root of the tongue connects to the epiglottis via three folds of mucosa: a single, median glosso-epiglottic fold, and paired lateral glosso-epiglottic folds. Between the median and lateral glosso-epiglottic folds are the epiglottic valleculae. These shallow depressions help to prevent saliva from being aspirated during breathing.

Photo 9. Glosso-epiglottic folds and epiglottic valleculae

8.) On one side of the donor, remove the mucous membrane of the tongue on the dorsal and inferior surfaces to locate the intrinsic muscles of the tongue.

Note:  The intrinsic musculature of the tongue originates and inserts within the tongue, and thus controls the tongue’s shape for speech and mastication. All intrinsic tongue muscles are innervated by the hypoglossal n. (CN XII). Intrinsic tongue muscles include: superior longitudinal m., inferior longitudinal m., transverse m., and vertical m.

Note: Superior longitudinal m. consists of thin wisps of fibers running just deep to the dorsal mucosa from the root of the tongue, (adjacent to the epiglottis) to the apex.

Note: Inferior longitudinal m. consists of thin wisps of fibers running between the genioglossus m. and the hyoglossus m. from the root of the tongue (adjacent to the hyoid bone) to the apex.

Note: Transverse m. connect the median fibrous septum to the margins of the tongue.

Note: Vertical m. are robust fibers connecting the dorsal and inferior aspects of the body of the tongue.

Photo 10. Intrinsic muscles of tongue

9.) Identify the gross features of the oral cavity proper: lingual frenulum, sublingual fold (& openings of the sublingual ducts), sublingual caruncle, and fimbriated folds.

Note: The lingual frenulum connects the inferior midline of the tongue to the mucosa of the floor of the oral cavity. It may be highly variable in size and attachment. In some individuals a shortened and thickened lingual frenulum may limit the mobility of the tongue, a condition known as ankyloglossia (‘tongue-tie’). Ablation of the lingual frenulum (frenulotomy) is less frequently performed to aid in difficulties with speech, but it may increase success of latching for breast feeding. The lingual frenulum may not be present if the head was exactly sectioned in the midline, but should be present if slightly off midline. If unavailable on the donor, the frenulum of the tongue can be identified on your lab partners.

Note: The sublingual folds are formed by the sublingual glands and ducts of the submandibular glands shaping the mucosa. Along these folds are the bilateral openings of the sublingual ducts.

Note: The sublingual caruncle is situated at the confluence of the sublingual folds and the lingual frenulum. The sublingual caruncle is the location where the submandibular (Wharton’s) ducts secrete saliva into the oral cavity.

Note: Fimbriated folds flank the lingual frenulum on the inferior surface of the tongue. Typically, the lingual veins are visible deep to the inferior surface mucosa between the lingual frenulum and the fimbriated folds.

Photo 11. Lingual frenulum and sublingual: fold and caruncle

Examine the oral cavity proper and dissect the sublingual space - SUPERFICIAL SIDE

Find these structures:

• Sublingual gland

• Submandibular gland, deep portion

  • Submandibular (Wharton’s) duct

• Lingual n. (V3)

  • Submandibular ganglion

• Hypoglossal n. (CN XII)

• Vena comitans of hypoglossal n.

• Lingual a.

10.) Reflect the tongue posteromedially to expose the floor of the mouth in the oral cavity proper.

Note: The floor of the mouth, deep to the oral mucosa is the sublingual space. The sublingual space is a potential space, superior to the mylohyoid mm., bounded laterally by the mandible, and posteriorly by the attachments of muscles to the hyoid bone. The sublingual space is continuous with the submental, submandibular, and buccal spaces.

11.) Clean and identify structures: sublingual gland, deep portion of submandibular gland, submandibular (Wharton’s) duct, lingual a. (& brs), lingual n. (& brs), submandibular ganglion, hypoglossal n. (CN XII), and vena comitans of hypoglossal n.

Note: Of the three major salivary glands, the sublingual gland is the smallest. It is located superior to the mylohyoid m. and when covered with mucosa, it forms the sublingual fold. These glands drain via numerous small ducts along the sublingual folds. The deep, smaller part of the submandibular gland is also located in this area and is closely associated with the posterior end of the sublingual gland.

Note: The mylohyoid line of the mandible is formed by the attachment of the mylohyoid m. The two salivary glands in this region are associated with this line: sublingual gland superior, and submandibular gland inferior.

Note: The lingual a. is typically the second branch of the external carotid a. that leaves the external carotid anteriorly. Passing between the hyoglossus m. and the middle pharyngeal constrictor m., the lingual a. supplies the floor of the oral cavity and the tongue. The lingual a. produces several branches, chiefly:

• Dorsal lingual brs. - arise medially to the hyoglossus m., supply the posterior tongue, soft palate, and palatine tonsil,

• Sublingual a. - arise anteriorly to the hyoglossus m., supplies the sublingual gland, and muscles and tissues of the floor of the oral cavity, and

• Deep lingual a. - the terminal br. of the lingual a., lies along the inferior margin to the tip of the tongue, supplies the anterior tongue.

Nearly all of the lingual a. branches anastomose with their contralateral paired artery along the midline.

Note: Deep to the mucosa in the oral cavity proper, the lingual n. and submandibular duct cross. The lingual n. descends into the oral cavity and loops under the submandibular duct to provide general sensory innervation to the anterior 2/3rds of the tongue.

Note: The submandibular (Wharton’s) duct traverses the space between the submandibular gland and sublingual caruncle. The duct is located between the hypoglossal n. and lingual n. in association with the hyoglossus m. The lingual n. passes deep to the duct about midway in the oral cavity.

Note: The lingual n. is an afferent branch of the posterior trunk of V3. It traverses the infratemporal fossa medial to the inferior alveolar n., where it is joined by the chorda tympani n. (branch of facial n., CN VII). Chorda tympani carries presynaptic parasympathetic fibers to the submandibular gland and taste to the body of the tongue (excluding the vallate papillae). The lingual n. enters the oral cavity superior to the mylohyoid m., and enters the tongue to provide sensory innervation to the body of the tongue and the floor of the oral cavity.

Note: In regards to innervation of the tongue, often the tongue is described in 2 sections: the anterior 2/3rds (innervated by facial n.) and the posterior 1/3rd (innervated by glossopharyngeal n.). The division between these sections is approximately the terminal sulcus; however, the area supporting the vallate papillae is innervated by the glossopharyngeal n. (CN IX).

Note: The submandibular ganglion is delicately associated with the lingual n. and is superior to the deep portion of the submandibular gland. This ganglion is one of four named peripheral parasympathetic ganglia (ciliary, pterygopalatine, submandibular, and otic). The submandibular ganglion receives preganglionic parasympathetic fibers from the chorda tympani, a branch of the facial n. (CN VII). Postganglionic parasympathetic fibers leave the ganglion to innervate the submandibular and sublingual glands, among other smaller glands (e.g. anterior lingual) by means of the lingual n., a branch of V3.

Note: The vena comitans of hypoglossal n. is a tributary of the lingual v. This vein accompanies the hypoglossal n. (CN XII) inferiorly along the hyoglossus m.

Photo 12. Oral cavity proper

Photo 13. Oral cavity proper

Section cervical vertebrae to view posterior pharynx and esophagus

Find these structures:

• Pharynx

• Esophagus

• Hyoid bone

  • Greater horns (cornu)

12.) Locate the intervertebral disc between C7-T1, and work from this level superiorly. Remove any remaining back muscles. Be careful to maintain sternocleidomastoid mm. and accessory nn. (CN XI). Deep neck musculature (e.g. semispinalis mm.) must be removed.

13.) If necessary, complete laminectomy to C1. Remove any remaining spinal cord.

14.) Lift the esophagus, pharynx, other viscera, and neurovasculature anteriorly to separate from the anterior vertebral column. DO NOT SKIP THIS STEP!

Photo 1. Procedural: separating soft tissues from the vertebral column

15.) Chisel through the C7-T1 intervertebral disc.

16.) Disarticulate the superior articular facets of C1 from the occipital condyles. Use scissors or bone cutters to cut through the connective tissues which surround this joint. If this does not provide enough separation, insert a chisel into the space between the bones, and gently twist.

17.) Using an autopsy (Stryker) saw, complete a mid-sagittal section of the vertebral bodies of C1-C7. Reflect the sectioned portions of the vertebrae laterally to expose the posterior pharynx and esophagus.

Photo 2. Procedural: using autopsy saw

Photo 3. Procedural: vertebrae reflected, posterior pharynx and larynx

18.) Palpate the greater horns of the hyoid bone. These will be important landmarks in distinguishing the pharyngeal constrictor muscles.

Photo 4. Greater horns of hyoid bone and posterior pharynx

Clean and distinguish pharyngeal mm.

Find these structures:

• Superior pharyngeal constrictor mm.

• Stylopharyngeus mm.

• Middle pharyngeal constrictor mm.

• Inferior pharyngeal constrictor mm.

  • Thyropharyngeal part

  • Cricopharyngeal part

• Pharyngeal (neural) plexus

  • Glossopharyngeal n. (CN IX)

  • Vagus n. (CN X)

• Ascending pharyngeal a. (br. of external carotid a.)

19.) Locate and carefully clean the stylopharyngeus mm. On the posterior surfaces of the stylopharyngeus mm., locate the glossopharyngeal nn. (CN IX).

Note: Stylopharyngeus m. is one of three internal pharyngeal muscles with longitudinally (obliquely)-oriented fibers. Portions of this muscle are visible from an external view due to its attachment site on the styloid process of the temporal bone. Unlike the other pharyngeal muscles, which are innervated by branches of vagus n. (CN X), stylopharyngeus m. is innervated by glossopharyngeal n. The glossopharyngeal n. (CN IX) also afferently (sensory) innervates most of the pharynx. The stylopharyngeus m. attaches the styloid process of the temporal bone to the superior margin of the thyroid cartilage. The muscle runs between the superior and middle pharyngeal constrictor mm., thus it is a helpful landmark of the posterior pharynx.

Photo 5. Stylopharyngeus m. and glossopharyngeal n.

20.) Clean and distinguish the pharyngeal constrictor muscles.

Note: There are three (pharyngeal constrictor) muscles in the external layer of the pharynx, all of which have circularly-oriented fibers. The pharyngeal constrictors surround the pharynx, and meet along a posterior midline pharyngeal raphe.

Note: Distinguishing between the pharyngeal constrictor mm. can be difficult. The superior and middle pharyngeal constrictor mm. are distinguished by the muscle belly of the stylopharyngeus m., which inserts between these muscles. The middle and inferior pharyngeal constrictor mm. are more difficult to visually distinguish. The fibers of the middle pharyngeal constrictor mm. attach to the hyoid, whereas the inferior pharyngeal constrictor mm. attach to the thyroid and cricoid cartilages.

Photo 6. Pharyngeal constrictor mm. and stylopharyngeus m.

Note: The pharynx is supported by two associated bodies of fascia: pharyngobasilar fascia and buccopharyngeal fascia. The pharyngobasilar fascia (the deep investing/epimysial layer of the external pharyngeal mm.) suspends the superior pharyngeal constrictor m. from the basilar part of the occipital bone and the adjacent temporal bone. The pharyngobasilar fascia is closely associated with the pharyngeal raphe at the pharyngeal tubercle. The buccopharyngeal fascia (the superficial investing/epimysial layer of the external pharyngeal mm.) consists of a thickened epimysium of the superior pharyngeal constrictor that extends anteriorly from the pharyngeal raphe to the superficial surface of the buccinator m. (of the cheek). A condensed band of the buccopharyngeal fascia that extends from the pterygoid hamulus to the posterior end of the mylohyoid line of the mandible is the pterygomandibular raphe. The pterygomandibular raphe connects the buccinator m. to the superior pharyngeal constrictor m.

Image 1. Pterygomandibular raphe

Note: The superior pharyngeal constrictor m. consists of four parts, each arising from a distinct location (associated by name), and coalescing posteriorly to the superior portion of the pharyngeal raphe. The four distinct parts (and their anterior attachments) include the:

• • pterygopharyngeal part (pterygoid hamulus & occasionally the posterior aspect of the medial pterygoid plate),

• mylopharyngeal part (posterior portion of mylohyoid line of mandible), and the 

• buccopharyngeal part (pterygomandibular raphe),

• glossopharyngeal part (posterolateral tongue).

Note: The middle pharyngeal constrictor m. originates on the hyoid bone (greater and lesser horns) and the stylohyoid ligament, and inserts on the pharyngeal raphe.

Note: The inferior pharyngeal constrictor m. consists of two parts. These parts (and their attachments) include the:

• • thyropharyngeal part (thyroid cartilage of the larynx), and the

• cricopharyngeal part (cricoid cartilage of the larynx).

Note: The pharyngeal constrictor mm. are innervated by the pharyngeal (neural) plexus, which receives efferent (motor) fibers from the vagus nn. (CN X) and afferent (sensory) fibers from the glossopharyngeal nn. (CN IX). The cricopharyngeal part of the inferior pharyngeal constrictor m. receives dual innervation from the pharyngeal (neural) plexus and the vagus n. (CN X) via the recurrent laryngeal n. and the superior laryngeal n. (Sakamoto, 2013). When activated, the pharyngeal constrictors serially constrict the lumen of the pharynx. Some fibers of the middle pharyngeal constrictor mm. can also act as an elevator of the pharynx (Sakamoto, 2014). The plexus also receives autonomic fibers from the vagus n. (parasympathetic) and superior cervical ganglion (sympathetic).

Note: The pharyngeal constrictor mm. are primarily supplied by the ascending pharyngeal a., a branch of the external carotid artery. Branches from the inferior thyroid a. also may supply the inferior pharyngeal constrictor m. Both superior and middle pharyngeal constrictor mm. may be partially supplied by tonsillar br. of the facial artery (also a branch of the external carotid a.). The superior pharyngeal constrictor m. may also receive blood from the ascending palatine a. (a br. of the facial a.).

Note: The pharyngeal constrictor muscles are drained of blood by the pharyngeal venous plexus, which drains into the internal jugular vv.

Locate the cervical sympathetic trunk, and identify the superior cervical ganglion

Find these structures:

• Cervical sympathetic trunk

  • Superior cervical ganglion

  • Middle cervical ganglion

  • Inferior cervical ganglion

21.) Locate and clean the superior cervical ganglion at the C1/C2 level. The superior cervical ganglion is quite large (long), and is associated with gray rami communicantes for C1-4. Inferior to the ganglion, follow the cervical sympathetic trunk. Locate the middle cervical ganglion near the C5/C6 level. Locate the inferior cervical ganglion at the C7/T1 level.

Note: The sympathetic division of the autonomic nervous system consists of pre- and postganglionic fibers which typically (but not always) synapse in ganglia of the sympathetic trunk. Preganglionic fibers travel from the intermediolateral (IML) nucleus (lateral horn) of the spinal cord, out via the ventral roots of spinal nerves to the ventral primary rami (VPR), and then leave the spinal nerves via white rami communicantes (at levels T1-L2) to the sympathetic trunk. Once in the trunk, preganglionic fibers may:

• synapse,

• leave the trunk as part of a splanchnic nerve (without synapsing), or

• ascend or descend the sympathetic trunk (and then either synapse, or leave the trunk).

From the synapse, postganglionic fibers carry signals back to the VPR of the spinal nerve via gray rami communicantes. These fibers can then be distributed by the VPR. While white rami communicantes are restricted to the T1-L2 levels, the sympathetic trunks extend the entire length of the spinal cord, and gray rami communicantes conduct postganglionic fibers back to VPRs at every level of the cord. In the neck, there are typically 2-3 sympathetic ganglia, whereas in the thorax there are typically sympathetic ganglia at every spinal level (T1-T12).

Note: The cervical sympathetic trunk and ganglia are found in close posteromedial association with the carotid sheath.

Note: The middle cervical ganglion is typically absent. When present, it is usually found adjacent to the inferior thyroid a. near the C5-C6 level.

Note: The inferior cervical ganglion frequently combines with the first (T1) thoracic ganglion, and sometimes the second-fourth (T2-4) thoracic ganglia. When this happens, the resulting fused ganglia are called the cervicothoracic ganglion or stellate ganglion.

Photo 8. Superior cervical ganglion and cervical sympathetic trunk

Photo 9. Cervical sympathetic ganglia

Remove the posterior portion of the carotid sheath, and identify the contents

Find these structures:

• Common carotid a.

• Carotid sinus

• Carotid body

  • Internal carotid a.

  • External carotid a.

    • Ascending pharyngeal a.

    • Superior thyroid a.

      • Superior laryngeal a.

• Thyrocervical trunk

  • Inferior thyroid a.

    • Inferior laryngeal a.

• Vagus n. (CN X)

  • Superior laryngeal n.

    • External br.

    • Internal br.

  • Recurrent laryngeal n.

22.) Position (but do NOT remove) the superior cervical ganglion and sympathetic trunk laterally. Remove the posterior carotid sheath, and locate the internal jugular v., common carotid a., and vagus n.

Photo 10. IJV, common carotid a., & vagus n.

23.) Locate the branches of the vagus n. (CN X) in this region, specifically the superior laryngeal n. (external and internal brs.) and recurrent laryngeal n.

Note: Superior laryngeal n. typically branches from vagus n. (CN X) superior to the carotid bifurcation. Internal br. of superior laryngeal n. afferently (sensory) serves the mucosa of the: laryngeal vestibule, middle laryngeal cavity, and superior surface of the vocal folds. This branch is accompanied by the superior laryngeal a. (a branch of superior thyroid a.). The external br. of superior laryngeal n. efferently (motor) serves the inferior pharyngeal constrictor m. and cricothyroid m.

Photo 11. Superior laryngeal n. (external & internal brs.) and superior laryngeal a.

Note: The recurrent laryngeal n. efferently serves all intrinsic mm. of the larynx, except cricothyroid m., and afferently serves (and is secretomotor to) the mucosa of larynx below vocal folds. The portion of the recurrent laryngeal n. superior to the border of the cricoid cartilage is synonymous with the inferior laryngeal n.

Photo 12. Recurrent laryngeal n.

24.) Locate the carotid bifurcation. Differentiate between the external and internal carotid aa. Locate the carotid body and carotid sinus.

Note: The bifurcation of the common carotid a. typically occurs at the level of C3-C4 or the superior border of the thyroid cartilage.

Note: The carotid body is typically located on the deep side of the bifurcation of the common carotid a. and should be slightly darker than the surrounding connective tissue. The carotid body (a chemoreceptor) functions in monitoring oxygen levels in the blood.

Note: The carotid sinus is typically a dilation of the internal carotid a., just superior to the carotid bifurcation, or at the bifurcation. The sinus functions to monitor blood pressure via baroreceptors in its walls.

Note: The carotid branch of the glossopharyngeal n. (CN IX), and the vagus n. (CN X) afferently (sensory) serve both the carotid sinus and body.

Photo 13. Carotid bifurcation

25.) Follow the external carotid a. superiorly, and locate the superior thyroid a. (found previously) and its branch, the superior laryngeal a. Superior to the superior thyroid a., you may see more branches of the external carotid a. to be dissected in future labs.

Note: The superior thyroid a. is typically the first anterior branch of the external carotid a., and descends to the thyroid gland.

Note: The superior laryngeal a. accompanies the internal br. of superior laryngeal n.

Note: The lingual a. and facial a. are anterior brs. of the external carotid a., and are typically the largest of the external carotid branches. The lingual a. is located near the middle pharyngeal constrictor m. The facial a. branches from the external carotid a. in a common branch with or just superior to the lingual a. Both arteries will be dissected in more detail in subsequent labs.

Photo 14. External carotid a. and branches

26.) Locate the thyrocervical trunk (first part of the subclavian a., as seen in previous labs). Find the inferior thyroid a., and then locate its branch to the larynx (the inferior laryngeal a.).

Photo 15. Inferior laryngeal a.

Dissect internal pharynx and esophagus

Find these structures:

• Nasopharynx (margins: choanae - soft palate)

• Oropharynx (margins: soft palate - superior margin of epiglottis & pharyngo-epiglottic folds)

  • Uvula

  • Root of tongue & lingual tonsil

• Laryngopharynx (margins: superior margin of epiglottis & pharyngo-epiglottic folds - inferior margin of cricoid cartilage)

  • Epiglottis

  • Entrance to esophagus

27.) Make a sagittal section along the posterior aspect of esophagus and pharynx (along the pharyngeal raphe), extending as far superiorly as possible. Locate the naso-, oro-, and laryngopharynx.

Note: The soft palate is the superior boundary of the oropharynx. The uvula is the posteroinferior, free process of the soft palate situated in the superior portion of the oropharynx.

Note: The root of the tongue is located inferior to the uvula in this view. The lingual tonsil is composed of multiple lymphoid nodules on the posterior aspect of the dorsum of the tongue. These cause the rugose appearance on the back of the tongue.

Photo 16. Oropharynx

Note: The epiglottis is the superior boundary of the laryngopharynx and is posterior to the root of the tongue.The epiglottis is composed of epiglottic cartilage covered by mucous membrane. During swallowing, the epiglottis closes inferiorly to cover the elevated larynx to close off access into the larynx.

Note: The entrance to the esophagus is located approximately at the level of C6 or the inferior border of the cricoid cartilage.

Photo 17. Laryngopharynx

27.) Remove the mucosal layer of the laryngopharynx to expose the posterior aspect of the larynx.

Photo 28. Procedural : removal of mucosal layer of larynx  

28.) Identify the muscles of the posterior larynx.

Note: The oblique and transverse arytenoid muscles attach posterior surfaces of contralateral arytenoid cartilages. Some sources consider these two muscles parts of one unified arytenoid muscle. Some superior fibers of the oblique arytenoid m. continue and wrap around the arytenoid cartilage into the ary-epiglottic fold. These fibers are the ary-epiglottic part of the oblique arytenoid m. When activated, the oblique and transverse arytenoid mm. adduct the vocal processes of the arytenoid cartilages, which combined with the lateral crico-arytenoid muscles, closes the glottis.

Note: The posterior crico-arytenoid muscles are the sole abductors of the vocal processes of the  arytenoid cartilages, which opens the glottis.

Photo 29. Arytenoid mm. & posterior crico-arytenoid m.

29.) Reflect the inferior pharyngeal constrictor mm. laterally from the thyroid cartilages. Locate the cricothyroid m. The larynx will need to be rotated laterally to view this muscle. 

Photo 30. Cricothyroid m. 

30.) Remove the pharyngeal mucosa of the ary-epiglottic folds superior to the oblique and transverse arytenoid mm. to reveal the arytenoid cartilages and lateral crico-arytenoid mm.

Note: The arytenoid cartilages sit atop the superior margin of the lamina of the cricoid cartilage. Each arytenoid cartilage has an anteriorly positioned vocal process and a laterally positioned muscular process. Vocal ligaments attach the laminae of the thyroid cartilage to the vocal processes of the arytenoid cartilages. Muscular processes offer a location for attachment of intrinsic laryngeal muscles. Many of these muscles will rotate (or medially glide) the arytenoid cartilages to either adduct the vocal ligaments (narrow the rima glottidis) or abduct the vocal ligaments (expand the rima glottidis).

Photo 31. Lateral crico-arytenoid m. 

31.) Turn the donor supine, and locate the thyrohyoid membrane and cricothyroid m. 

Note: Cricothyroid mm. are located on the anterolateral larynx between the thyroid and cricoid cartilages. These muscles will tilt the thyroid cartilage anteriorly at the cricothyroid joint, which lengthen (and thus tense) the vocal ligaments. The cricothyroid m. is innervated by the external br. of the superior laryngeal n. Recall that all other intrinsic laryngeal muscles are innervated by the recurrent laryngeal n.

Photo 32.  Thyroid membrane and cricothyroid m. 

32.) Reflect the cricothyroid muscle unilaterally, and locate the cricothyroid joint.

Note: The paired, cricothyroid joints are synovial and important in rotational movements, which will lengthen (adds tension) to the vocal ligaments. These joints are located on the lateral portions of the larynx between the lateral lamina of the cricoid cartilage and inferior horn of the thyroid cartilage.

Photo 33. Cricothyroid joint

33.) Using sharp-sharp scissors, mid-sagittally section the thyroid cartilage.

34.) With the donor prone, disarticulate (cut) a single cricothyroid joint and reflect the posterior edge of the ipsilateral thyroid lamina anteriorly (toward the anterior midline) to reveal a closer view of the lateral crico-arytenoid m.  

Note: The lateral crico-arytenoid m. runs obliquely along the lateral surface of the cricoid, ascending toward its attachment to the muscular process of the arytenoid cartilage. 

Photo 34. Lateral crico-arytenoid m. 

35.) Make a midsagittal cut from the posterior laryngeal inlet inferiorly through the cricoid cartilage to open the larynx and visualize internal structures. Retract the sides of the larynx laterally. Locate the laryngeal cartilages from an internal view.

Photo 35. Procedural: Cutting posterior larynx 

Photo 36. Internal Larynx

36.) Locate the laryngeal vestibule, vestibular folds, rima vestibuli, laryngeal ventricle, vocal folds, rima glottidis, and infraglottic cavity.

Note: The laryngeal vestibule is located between the inlet to the larynx and the vestibular folds.

Note: The vestibular folds are often referred to as the false vocal folds or ventricular folds. The folds are composed of the vestibular ligaments (inferior parts of the quadrangular membranes) covered with mucosa. These folds are located superior and lateral to the vocal folds. These folds are involved in the production of some sounds (e.g. throat singing), but are not associated with speech.

Note: The laryngeal ventricle is the space between the vestibular folds and the vocal folds. 

Note: The vocal folds are often referred to as the true vocal folds/cords. The folds are composed of vocal ligaments and muscles covered with mucosa, and flank the rima glottidis. These folds are important in sound production. The rima glottidis changes width depending on position of the arytenoid cartilages and vocal folds.

Note: The infraglottic cavity is located inferior to the rima glottidis and vocal folds and superior to inferior border of the cricoid cartilage.

Photo 37. Internal Larynx 

37.) On one side, remove the mucosal lining of the larynx to expose the contents of the vocal folds (vocalis m., vocal ligament, and thyro-arytenoid m.) and the remainder of the conus elasticus.

Note: Two sheets of fibroelastic connective tissue help to give shape to the walls of the larynx and laryngeal features: the quadrangular membrane and the conus elasticus. 

Note: The conus elasticus is a fibroelastic sheet, that shapes the walls of the larynx as a funnel between the thyroid and cricoid cartilages. The superior-most aspects of the conus elasticus are the vocal ligaments and the walls of the laryngeal ventricle. The anteromedial aspect of the conus elasticus is the (median) cricothyroid ligament, the connective tissue pierced during a cricothyrotomy. 

Note: The thyro-arytenoid m. and vocalis m. attach the anterior aspects of the arytenoid cartilages to the posterior aspect of the laminae of the thyroid cartilage. The vocalis m. is immediately lateral to (and has fibers inserting on) the vocal ligament. The thyro-arytenoid m. runs lateral and parallel to the vocalis m. Some sources consider the vocalis m. as specialized fibers of the thyro-arytenoid m. The thyro-arytenoid mm. pull the arytenoid cartilages toward the thyroid cartilage, thus decreasing tension on the vocal ligaments (lowers pitch). Vocalis mm. add lateral tension to the vocal ligaments (finely increases pitch and timbre). 

Note: Fibers of the thyro-arytenoid m. extend beyond the arytenoid cartilage into the ary-epiglottic fold. Some of these fibers, known as the thyro-epiglottic part of the muscle, may continue through the ary-epiglottic fold into the margin of the epiglottis. When activated, the thyro-epiglottic parts widen the laryngeal inlet. 

Photo 38. Thyro-arytenoid m., vocalis m., and vocal ligament 

38.) On the ipsilateral side, continue to remove the mucosal lining of the larynx superiorly to uncover the quadrangular membrane, and its vestibular ligament. 

Note: The quadrangular membrane is a poorly defined fibroelastic sheet spanning the space between the lateral margins of the epiglottis and the arytenoid cartilages. The inferior-most extent of the quadrangular membrane forms the vestibular ligaments. 

Photo 39. Quadrangular membrane 

Observe the relationships of the larynx to surrounding structures

Find these structures:

• Thyrohyoid membrane

• Trachea

  • Cricotracheal ligament

  • Tracheal cartilages

  • Trachealis (m.)

39.) With the donor supine, investigate the relationships of the larynx to the hyoid bone and the trachea. 

Note: The thyroid cartilage is suspended from the hyoid bone by the thyrohyoid membrane. The superior laryngeal a. & v., as well as the internal branch of the superior laryngeal n., pierce the thyrohyoid membrane through a common opening.

Photo 40. Thyrohyoid membrane 

Note: The cricoid cartilage helps to suspend the trachea inferiorly via the cricotracheal ligament. 

Note: The trachea connects the larynx to the primary bronchi of the lungs. The trachea begins at the inferior margin of the cricoid cartilage (near C6), and ends at the tracheal bifurcation in the superior mediastinum (near T4/5). The trachea sits anterior to the esophagus in the neck and mediastinum, and may be palpated in the neck. The trachea consists of a series of 16-20 ‘C-shaped’ hyaline cartilages connected by fibroelastic connective tissue. The posterior aspect of the trachea (where the cartilages are incomplete) is comprised of a fibromuscular membrane containing trachealis muscle, smooth muscle that can alter the diameter of the lumen of the trachea. 

Photo 41. Tracheaa

40.) Just proximal to the tracheal bifurcation, excise (with two transverse cuts) a 4-5 cm. section of the trachea, and examine its features.

Photo 42. Trachea 

Photo 43. Trachealis m.