110 DISSECTION OP THE DOG 



membraneous part is wider. On the dorsal wall of the prostatic part, moreover, 

 an elongated ridge, the crista urethralis and colliculus seminalis, will be noticed ; 

 and on each side of the ridge the opening of the ductus deferens and the 

 numerous openings of the ducts of the prostate will be found. 



M. ischio-cavernosus. — The ischio-cavernosus muscle is short and broad, 

 and covers the crus penis. Its fibres arise from the dorsal aspect of the medial 

 angle of the sciatic tuber, and are spread out over the expanded portion of the 

 corpus cavernosum penis. 



M. bulbo-cavernosus. — The bulbo-cavernosus muscle of the dog is well 

 developed. It consists mainly of transverse fibres covering the bulbus urethrse, 

 and is connected with the middle part of the sphincter muscle of the anus. 



M. retractor penis. — The long, pale retractor of the penis leaves the aboral 

 part (possibly also the middle portion) of the sphincter ani, and runs along the 

 urethral surface of the penis towards the glans. 



M. ischio-urethralis. — The ischio-urethral muscle is rather small, and 

 springs from the dorsal aspect of the medial angle of the sciatic tuber. The 

 fibres of the muscle pass to the symphysis of the ischium and are inserted 

 into a fibrous ring through which pass the dorsal veins of the penis. 



M. urethralis. — As has already been mentioned, the pelvic portion 

 of the urethra is surrounded by a circular muscle, which can now be 

 demonstrated as continuous with the bulbo-cavernosus muscle. 



A. hypogastrica. — One of the terminal branches of the abdominal aorta, 

 the hypogastric artery pursues an oblique caudo-lateral course across the 

 brim of the pelvis. Between it and the middle sacral artery is a group of 

 lymph -glands (lymphoglandulee iliacse). Scarcely has the hypogastric artery 

 reached the pelvic cavity than it divides into two parts, which may be 

 called, from their distribution, the one visceral, the other parietal. 



The artery crosses the ventral aspect of the common iliac vein obliquely. 

 The ilio-psoas muscle lies on its lateral side, and ventrally it is separated 

 from the terminal part of the colon by peritoneum only. 



A. umbilicalis. — The only collateral branch of the hypogastric is the 

 umbilical artery, which proceeds towards the side of the vertex of the bladder 

 in the lateral peritoneal fold connected with this viscus. A cranial vesical 

 artery (a. vesicalis cranialis) arises from the umbilical, and supplies both the 

 bladder and the prostate. A small branch, the a. defer entialis, follows the 

 deferent duct for some distance. 



A. pudenda interna. — The visceral part (pars visceralis) of the hypo- 

 gastric artery consists solely of the internal pudendal artery, which travels at 

 first alongside the rectum — from which it is separated by peritoneum — 

 then across the lateral face of the coccygeus and levator ani muscles within 

 the sciatic spine, to bend round the arch formed by the ischia, and, finally, 

 to be continued as the dorsal artery of the penis. 



The following are the branches of the internal pudendal artery : (1) The 



