The penis of the bull is fibroelastic, which means that an erection is achieved by extension of the penis as opposed to engorging the penis with blood. The image displayed is a cross section of the penile shaft, or the main portion of the penis. The major tissues are labeled as follows:

• CC - Corpus Cavernosum. Erectile tissue which fills with blood during erection. Easily identified due to the prominent sinuses.

• CS - Corpus Spongiosum. Erectile tissue which surrounds the urethra and prevents compression of urethra by the corpus cavernosum

• PU - Penile Urethra. Lumen which delivers urine and semen from within the body. Identifiable as the major duct of the penis, found closer to the ventral aspect of the penis.

The distal end of the penis is called the Glans Penis. It is specifically adapted to the reproductive system of the female member of the species.

The Sigmoid Flexure is a bend in the penile shaft inside the body. It maintains the penis within the body when not erect.

The vagina of the cow is comprised of the vestibule (or caudal vagina), cranial vagina, and vaginal fornix. The main function is to conduct genetic material to the cervix, where it will be delivered to the uterus and, eventually, the oviduct. The vagina contains ducts which serve to lubricate the entrance to the female reproductive system. The vestibule is common to the urinary and reproductive systems and is where the urethral orifice is located.

Shown in the image to the left are the three glands which produce seminal fluids:

• VG - Vesicular Glands. These glands contribute the majority of the seminal volume. They are lobulated and serve as a reservoir for the milky component of semen, providing fluid to conduct spermatozoa out of the body. They empty into the ejaculatory duct during ejaculation.

• BP - Body, or Corpus Prostate. The prostate gland is thought to provide chemical energy to spermatozoa.

• The Bulbourethral Glands in the bull are small. They are located under the bulbospongiosus muscle, located at the base of the penis (BP), and serve to lubricate and buffer the urethra in order for spermatozoa to pass through it.

The tracts of the bull's reproductive system carry spermatozoa from the epididymis to the distal end of the penis

• DD - Ductus Deferens. This is the pathway for spermatozoa to leave the testes. The ductus deferens is located within the spermatic cord.

• A - Ampullae. The term ampulla refers to the region of the ductus deferens which widens just proximal to the ejaculatory duct. This widening is due to an increase in the thickness of the mucosa of the ductus deferens, forming crypts.

The testis consists of a parenchyma which produces gametes. The ducts of the parenchyma empty into a region called the mediastinum, which brings spermatozoa to the head of the epididymis.

Before spermatozoa is ready to be ejaculated, it must mature. This process is called spermiogenesis, and occurs within the epididymis. The path is as follows:

• Caput Epididymis - Immature spermatozoa begin to lose cytoplasmic droplet. Rete fluid is removed from the lumen.

• EB - Epididymal Body, or Corpus Epididymis. Spermatozoa continue to mature. Concentrations remain relatively constant within this region.

• ET - Epididymal Tail, or Cauda Epididymis. Sperm complete maturation in the proximal tail, and when they move to the distal tail, they are mature and prepared for ejaculation.

The ductus deferens travels through the Spermatic Cord, which is comprised of several structures which support the testes:

• CM - Cremaster Muscle. This muscle is able to bring the testes toward the body for short periods of time. It plays a function in temperature regulation with the tunica dartos.

• The Pampiniform Plexus is a collection of vasculature. It plays a part in temperature regulation using a countercurrent heat exchange mechanism. Its primary function is to supply the testes with blood.

• The ductus deferens increases in diameter as it approaches the ejaculatory duct, where it empties. This widened part of the structure is called the Ampulla.

The male gonads, or testes, are surrounded by the scrotum, which is comprised of four layers:

• TA - Tunica Albuginea. Connective tissue capsule enveloping the testis - not part of the scrotum.

• VVT - Visceral Vaginal Tunic. Outer layer of testicular capsule.

• PVT - Parietal Vaginal Tunic. Envelops testicular capsule

• The Scrotal Fascia connects the vaginal tunics to the tunica dartos

• The Tunica Dartos is a muscular layer of the scrotum which elevates the testes to regulate temperature.

• The Scrotal Skin is the outer layer of the scrotum. It is integumentary tissue derived from the skin of the abdomen.

The ovary is the female gonad. It has endocrine and reproductive function, as it produces estrogen and progesterone as well as oocytes. The Antral Follicle (labeled AF) is a follicle that is selected for ovulation. It will fill with Antral fluid and eventually burst. The oocyte which ovulates from the follicle will then be picked up by the infundibulum and travel through the ampulla, where fertilization occurs, and the isthmus. These three terms refer to parts of the oviduct, also referred to as the fallopian tube.