670 



BLOOD-VASCULAE SYSTEM OF THE HORSE 



(1) The umbilical artery is given off from the internal pudic about an inch 

 (ea. 2-3 cm.) from the origin of that vessel. It is a very large artery in the 

 foetus, in which it curves downward and forward at the side of the bladder in the 

 edge of the lateral umbilical fold of peritoneum, passes through the umbilical open- 

 ing, becomes a component of the umbilical cord, and ramifies in the foetal placenta. 

 After birth it extends only to the vertex of the bladder arid is much reduced. Its 

 lumen is almost obliterated and its wall is very thick, giving the vessel a cord-like 

 character, hence it is commonly termed the round ligament of the bladder.^ It 

 gives off small vesical branches (Aa. vesicales craniales) to the bladder, and twigs 

 to the prostate and ductus deferens in the male. In the mare a small branch runs 

 forward along the ureter into the broad ligament of the uterus. 



(2) The middle haemorrhoidal or vesico-prostatic artery (A. hsemorrhoidalis 

 media) in the male arises usually near the prostate and runs backward lateral to 

 the rectum. It supplies branches to the rectum, bladder, urethra, and accessory 

 genital glands. In the female the homologous vessel is much larger and gives off 



the posterior uterine artery (A. 

 uterina caudalis). This runs for- 

 ward on the side of the vagina, to 

 which it gives branches, and rami- 

 fies on the body of the uterus, anas- 

 tomosing with the anterior, and 

 middle uterine arteries. (In some 

 cases this artery arises from the 

 internal iliac or the umbilical.) 



(3) The perineal artery (A. 

 perinei) is relatively small in the 

 male. It ascends at the side of the 

 anus, which it supplies, and gives 

 twigs to the bulbocavernosus mus- 

 cle and the skin of the perineum. 

 In the female it is large and is dis- 

 tributed to the anus and vulva, and 

 gives a large branch to the vestibu- 

 lar bulb. 



(4) The artery of the bulb (A. 

 bulbi urethras) may be regarded as 

 the direct continuation of the in- 

 ternal pudic in the male. It lies 



at the side of the urethra above the ischial arch, dips under the bulbo-cavernosus 

 muscle, and ramifies in the corpus cavernosum urethrae. Before doing so it gives 

 off a small branch which turns around the ischial arch to reach the dorsum penis, 

 and anastomoses with the deep branch of the obturator. 



(4 a) The artery of the clitoris (A. clitoridis) is the homologue in the female 

 of the preceding vessel, but is much smaller. It passes to the ventral surface of 

 the vulva with a branch of the pudic nerve, supplies the clitoris, and gives twigs to 

 the vulva. 



3. The lateral sacral artery (A. sacralis lateralis) arises at the lumbo-sacral 

 articulation (Fig. 576). It passes backward under the wing of the sacrum, then 

 along the pelvic surface of the bone below the ventral sacral foramina and the 

 nerves emerging from them, and is continued by the lateral coccygeal artery. The 

 branches are as follows : 



(1) Spinal branches (Rami spinales) enter the vertebral canal through the 



1 The obliteration in the adult extends a variable distance from the vesical end toward the 

 origin, but usually involves completely only a small part. 



Fig. 579. — Cross-section of Tail of Horse. 

 1, Dorso-lateral coccygeal vessels and nerve; 2, ventro-lateral 

 coccj'geal artery and nerve; 3, middle coccygeal artery; 4, sacro- 

 coccygeus dorsalis; 4'> sacro-coccygeus lateralis; 5, 5' , intertrans- 

 versales; 6, sacro-coccygeus ventralis; 7, recto-coccygeus; 5, 

 cocc\'geal fascia; 9, fibro-cartilage between fourth and fifth 

 coccygeal vertebrae. The veins are black. 



