112 DISSECTION OP THE DOG 



superficialis) has been noted before as supplying branches to the gluteal, gemelh, 

 internal obturator, quadratus femoris, adductor, biceps, semitendinosus and 

 semimembranosus muscles. 



V. hypogastbica. — The hypogastric vein differs from the artery of the 

 same name in not having distinct parietal and visceral parts. It has two 

 main tributaries, viz. the caudal gluteal vein and a common vessel formed 

 by the union of veins from the penis (dorsal and deep), the perineal vein, and 

 the middle hsemorrhoidal vein. 



The hypogastric vein thus formed lies lateral to, and midway between, 

 the parietal and visceral parts of the artery. Its collateral tributaries are 

 the cranial gluteal (often double), cranial vesical and ilio-lumbar veins 

 corresponding to the arteries with the same names. 



N. pttdbndtts. — The pudendal nerve is formed by roots from the first 

 and second sacral nerves. These join on the medial side of the hypogastric 

 vessels, and the nerve so produced accompanies the visceral part of the artery 

 (internal pudendal artery). There is a close connection between the pudendal 

 and posterior cutaneous femoral nerves. 



From the pudendal nerve the following branches take origin : (1) A 

 branch running vertically in a ventral direction from the parent nerve close 

 to its commencement, and supplying the urethra, prostate, and urinary 

 bladder ; (2) middle hcemorrhoidal nerve (n. hsemorrhoidalis media) ; (3) perineal 

 nerve (n. perinei) ; (4) dorsal nerve of the penis (n. dorsalis penis). The three 

 last mentioned follow the arteries of the same name. Prom the dorsal nerve 

 of the penis springs a twig, already noted, which follows the ventral face 

 of the membranous urethra to the prostate. 



Dissection. — Remove the pelvic organs. Cut open the rectum longitudinally 

 and observe the transverse folds of mucous membrane, which become 

 longitudinal as the anus is approached. The lumen of the tube wiU 

 be noted as greater than that of the colon. Cut open the para-anal 

 sinus. 



Clear away the fat from that pelvic wall which is yet intact. By removal 

 of the levator ani muscle, the internal obturator muscle will be exposed. 



Determine the constitution and branches of the sacral plexus. 



M. obttjbatoe iNTEBNT/s. — The internal obturator muscle is thin, and 

 lies on the ventral wall of the pelvis over the obturator foramen. Its origin 

 is from the pubis and ischium as they form the margin of the foramen. The 

 muscular fibres converge to a flat tendon which lies upon the gemelli muscles 

 and is attached to the femur within the trochanteric fossa. 



Nn. lumbales et nn. saceales. — The seven lumbar and three sacral 

 spinal nerves form a plexus which is simple at the commencement of the 

 lumbar region, but becomes increasingly complicated towards the sacral 



