Veterinary Andrology and Reproductive Techniques

PENIS AND PREPUCE

(Penis and Prepuce)

Penis

• The peins is the copulatory organ of the males.
• The penile body is largely composed of corpus cavernosum penis. The corpus cavernosum penis arises as a pair of crura or roots from the ischial arch under ischiocavernosus muscle.
• The corpus cavernosum penis is enclosed by a thick layer of tunica albuginea, which is made up of collagen fibers.
• Several trabeculae are sent from tunica albuginea to enter into the corpus cavernosum penis for the support of cavernous (cave like) tissue.
• Ventral to the corpus cavernosum penis and surrounding the penile urethra is smaller corpus spongiosum penis (also called corpus spongiosum urethrae).
• The corpus spongiosum penis in enlarged at ischial arch to form the penile bulb.
• The bulb is covered by bulbospongiosus muscle (also called bulbocavernosus muscle).
• The two corpora (corpus cavernosum penis and corpus spongiosum penis) have several spaces (blood sinusoids) regarded as enlarged capillaries and are continuous with veins in the penis. Distention of these spaces with blood causes penile erection.
• Ischiocavernosus muscle or erector penis muscle is a short paired muscle and helps penile erection by its compressing and pumping action.
• The retractor penis muscle is a smooth muscle and arises from sacral or first and second coccigeal regions, divides and meets again under the anus and attaches to the penis at the distal end of the sigmoid flexure with fibers extending dorsally on the penis.
• The thickened dorsal portion of this fibrous sheath is known as dorsal apical ligament of the penis.
• The retractor penis muscle draws the penis back into sheath by acting on sigmoid flexure.
• In bull, ram, and boar the penis is characterized by S-shaped curve, the sigmoid flexure.
• The sigmoid flexure is post-scrotal in bull and ram and pre-scrotal in boar. Sigmoid flexure is absent in horse.
• The penis of the bull is about 90 cm in length from its root to the tip of the glans. The diameter is about 4 to 5 cm on erection.
• The glans penis is 7.5 to 12.5 cm long and is rather pointed. The glans penis (terminal part) is pointed and slightly twisted.
• After intromission the spirally arranged fibrous penile and prepenile prepuce is stretched and this causes the penis to spiral encircled by a shallow groove called as fossa glandis which forms urethral sinus or diverticulum, dorsal to the urethral process.
• The diverticulum (sinus) is often filled with smegma and carries infection, causing contagious equine metritis. The retractor penis muscle is not as strong as in bulls.
• The penis of the ram is about 30 cm in length and 1.5 to 2.0 cm in diameter and is characterized by urethral process, which extends 4 to 5 cm beyond the glans penis.
• The penile length of the boar is about 45 to 55 cm. There is no glans penis but the cranial portion is twisted counter clockwise.

• The penile length of dog during non-erect condition varies from about 6.5 to 24 cm depending upon the size of the dog.
• The penis of dog has two separate corpora cavernosa (separated by a medial septum).
• The cranial free portion of the penis contains a bone called “os penis” which is grooved ventrally for urethral passage.
• The glams penis of the dog consists of two parts. The proximal one third part of the glans is “bulbus glandis” and the distal two third part is “pars longa glandis”.
• The proximal part “bulbus glandis” usually becomes engorged with blood after the penis enters the vagina of the bitch and the withdrawal of the penis is not possible for some time after service until erection subsides. 

 

• The penis of the cat is short and is directed caudally and ventrally.
• The urethra lies dorsally in the penis. The os penis is either absent or short. The bulbus glandis is also absent.
• The glans penis is also absent but the terminal part (about 1 cm) contains several spines (about 120) pointing backward.
• Because of the pain caused by these spines the queen emits a loud cry after service. 

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Prepuce

• The prepuce is double invagination of skin surrounding the free end of the penis, when not erect.
• The prepuce in the bull is about 35 cm long and 4 cm in diameter. The prepucial orifice is 5 to 7 cm behind umbilicus and is surrounded by tuft of hair.
• In the bulls of Indian breeds, the prepuce is in the form of pendulous sheath.
• The prepuce of the horse makes a double fold. The prepucial acavity is 15 to 20 cm deep and then there is second fold to form the prepuce proper.
• Prepucial ring is prominent in between the two prepucial folds.
• The prepuce of ram is similar to bull but is relatively short.
• The prepuce of boar has a diverticulum (pouch) dorsal to the prepucial orifice.
• This diverticulum is filled with urine, secretions and dead cells and thus produces typical odour.
• The blood supply to the penis is through internal pudendal artery (to the root of the penis, obturator artery (to the body of the penis) and the external pudendal artery which gives rise to dorsal artery of the penis after passing through the inguinal canal.
• The nerve supply to the penis is from autonomic nerves from pelvic plexus and from pudendal and hemorrhoidal nerves.
• The pudendal and hemorrhoidal nerves and the motor nerves for retractor penis muscles.
• The dorsal nerve of the penis is a branch of pudendal nerve and supplies sensory fibers to the glans penis. These sensory fibers provide the afferent side for the reflex of erection and ejaculation. The reflex centers for erection and ejaculation are located in the lumber portion of the spinal cord.

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