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Penis is a copulatory organ in male
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Terminal portion of penis which is freely moving within the sheath is called as glans penis
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Penis has got three parts
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Besides above classification, the penis may be classified into two parts (viz., pelvic internal and preputial external parts) on the basis of location.
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Further, the penis can also be divided into two parts (viz., protruded and non-protruded parts) on the basis of its protrusions.
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The well developed fibrous tissue of penis, is a characteristic feature of bovine, porcine, ovine and caprines.
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The well developed vascular sinuses and elastic fibres of penis is a characteristic feature of equine, canine and feline
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The vascular type of penis contains large ratio of erectile tissue.
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The salient physiological functions of penis are
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To provide stiffness through engorgement of numerous labyrinth of haemo-sinuses with inflow of blood on proper sexual stimulation.
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To locate the vulva of opposite sex during coitus.
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To ejaculate semen into female genitalia.
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To urinate.
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Body of penis consists of corpus cavernosum penis muscle which is surrounded by a thick connective tissue capsule called as tunica albuginea.
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Beneath the corpus cavernosum penis is the corpus cavernosum urethrae which surrounds the urethral orifice. These two muscles are spongy in nature and divided into many spaces. Erection of the penis is caused by distention of theses spaces with blood.
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Root of penis is formed by two crura that fasten the penis on either side of the ischiatic arch.
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- The ischio-cavernosus muscle or erector penis muscle is a short paired muscle from tuber-ischii and sacro-sciatic ligament that is inserted on the crura and body of the penis. This muscle causes erection of penis by its compressing and pumping action on the bulbous portion of the corpus cavernosum penis .
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Retractor penis muscle is a paired smooth muscle originates from 1st and 2nd coccygeal vertebra, divides and meets again below the anus.
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Retractor penis muscle is passing along the caudal ventral surface of the penis and attaches to the tunica albuginea of the penis. It draws the penis back into the sheath after ejaculation.
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The muscles of pelvic urethra include Urethral muscle which is a circular muscle consisting of dorsal and ventral layers of transverse fibres. It aids in ejaculation and micturition by its forcible contraction.
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The Bulbo-cavernous muscle extends from ischiatic arch to glans penis. It is a continuation of extra-pelvic urethra. It is thickest at the root of the penis. It empties the extra pelvic urethra.
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Associated structures of penis
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The penis has some specific associated structures.
Sigmoid flexure
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The sigmoid flexure is a ‘S’ shaped bent of penis which is characteristically found in cattle-bull, buffalo-bull, boar, ram, buck and some wild animals like giraffe.
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Usually sigmoid flexure is post-scrotal in most of species except boar where it is pre-scrotal.
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Its posterior portion is attached to the retractor penis muscle.
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During copulation the flaccid sigmoid flexure becomes straightened due to relaxation of retractor penis muscle.
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After copulation the sigmoid flexure takes its original “S” shape, due to contraction of retractor penis muscle.
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Os-penis (Os priapi or Baculum )
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The os-penis is characteristically found in male dog, ferrets and mink. It is occasionally present in tom-cat
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It is absent in other species. The size of os-penis is grown up as the age advances.
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It may be utilized as age-indicator.
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The os-penis of each species has a characteristic shape which serves as diagnostic taxonomic structures in certain livestock.
Cork screw penis
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This helps in intromission of boar penis in the genitalia of sow ( Cervical canal in sow is cork screw like).
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Phallus
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The phallus is the external extremity of male genitalia in place of penis which is a characteristic feature of boar. This helps is ejaculation.
Phalli
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The phalli are the external extremity of male genitalia in place of penis which is a characteristic feature of ducks and geese. This helps in intromission.
Penile papillae
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The penile papillae are located at anterior portion of penis which is a characteristic feature of tom-cat, hamster, house-mice and rat. This probably helps in ovulation.
Urethral sinus
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The urethral sinus is located around the end of penis which is characteristic feature of stallion. This contains urethral sinus diverticulum.
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Urethral sinus diverticulum
Urethral process
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The urethral process is a filliform appendage extending form the anterior portion of glans penis which is a characteristic feature in ram, buck and giraffe.
Blood supply
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Internal pudendal artery to the root of penis
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Obturator artery to the body of the penis
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External pudendal artery that gives rise to dorsal artery of penis – after passing through the inguinal canal.
Nerve supply
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Autonomic nerves of the pelvic plexus and haemorroidal and pudendal nerves. The sensory nerve fibres to the glans penis come from the dorsal nerve of the penis, The glans penis is plentifully supplied with nerves and nerve endings.
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