veterinary Male Genitalia (Animal)

 Male Genitalia

Scrotum:    

situated between penis & anus

cutaneous pouch;  scrotal septum formed by dartos = “smooth  

cutaneous muscle” 

 spermatic  fascia: internal = a fibrous membrane (fibrous tunic) bound to parietal vaginal tunic 

         external = areolar connective tissue within dartos

         

 cremaster  muscle—   from internal abdominal oblique   m.; attaches to     internal spermatic fascia

 (not  developed  in the cat — where a levator scroti m. attaches to   the scrotal     septum )

 Testis:    pl.=  testes

         

produces spermatozoa and testosterone; coated by tunica albuginea (thick, white, c.t. capsule) & enveloped by visceral vaginal tunic 

  blood vessels are tortuous & highly branched for counter-current heat exchange;

  histologically, seminiferous tubules connect to a rete testis which connects to efferent ductules. which converge at the cranial pole of the testis to form epididymis.

Epididymis: 

spermatozoa storage & maturation occurs within the epididymis;  single coiled duct: head  —>  body  —>  tail  —>  ductus  deferens

proper ligament of the testis  —  homologous with proper ligament of ovary

ligament of the tail of epididymis —  (embryonic gubernaculum) homologous with round ligament of uterus

Ductus Deferens:   pl.= ducti deferentes

enveloped by visceral vaginal tunic connected to mesoductus deferens; traverses inguinal canal, penetrates prostate, & empties into urethra at the colliculus seminalis; terminal end of the ductus deferens features an ampulla (except in cat & pig) that has glands in its wall.

Spermatic  cord = ductus deferens + testicular vessels + vaginal tunics & spermatic fascia.

Accessory Genital Glands:  contribute seminal fluid to

                                                            the ejaculate  prostate (body + disseminated components) — all males. 

 bulbourethral glands (paired,  at ischial arch)  — not dog.

         

(vesicular glands [seminal vesicles] — neither dog nor cat )

 glands in wall of terminal segment of ductus deferens — all males

Penis:

three regions: root (contains bulb of penis & crus of penis),  body,  

                         and free part

 the penis is composed of: 1) penile urethra, 2) erectile tissue & 3)

                                              extrinsic muscles

Three bodies of erectile tissue:

corpus spongiosum penis: unpaired;  surrounds urethra;  begins as bulb of penis at root of penis

corpus cavernosum penis: paired; main erectile organ     (fibroelastic tunica albuginea)

crus of penis at the root of the penis — attaches to ischial arch;  covered by the ischiocavernosus m.;  replaced by os penis within free portion (carnivores)

glans (corpus spongiosum glandis)

dog : pars longa glandis & pars bulbus glandis (covers whole free portion)

cat : glans thin and distal [note: proximal skin has penil spines (cornified  papillae)]

Extrinsic penile muscles:    

bulbospongiosus m. (unpaired)— covers the bulb of the penis;

           

ischiocavernosus mm.(paired)—  covers the crus of the penis;

           

ischiourethralis mm. (paired)— small, inserts on ring around dorsal vein of penis;

retractor penis mm.(paired but together at midline) —smooth muscle;

 Prepuce:

cutaneous sheath which contains free part of penis (domestic mammals) 

 fascicles of cutaneous trunci m. encircling preputial orifice (dog)      = (retractor) preputial m.

Process of Erection: dog

parasympathetic effect — arterial vasodilation and venous constriction;

 

inflow to penis exceeds outflow and blood accumulates in penis;

pressure increases within fibroelastic capsules of erectile bodies;  

pressure mechanically compresses internal veins to further impede outflow;

contraction of extrinsic penile mm. pumps blood in against the increasing pressure; ischiourethralis m. occludes dorsal vein of penis to expand pressure within glans;

           

following intromission, the   superficially located dorsal veins   of penis, which drain

           

 the glans, are mechanically constricted. In the dog, the bulbus glandis expandsfollowing  intromission and this explains the  “tie” during copulation.

Ejaculation: 

          sympathetic pathway — contraction of ductus deferens, smooth m. in prostate & other glands, and internal urethral  sphincter (to prevent reflux   into bladder)

           also, contraction of urethralis m.& extrinsic penile mm.       

          propels ejaculate along urethra.