THE INTERNAL ILIAC ARTERY 



575 



upward at the sitle of the anus, whicli it supplies, and gives twigs to the bulbo- 

 cavernosus muscle and the skin of the perineum. In the female it is large and is 

 distributed to the anus and vulva, and gives a large branch to the vestibular bulb. 



(4) The artery of the bulb (A. bulbi urethra) may be regarded as the direct 

 continuation of the internal inidic in the male. It lies at the side of the urethra 

 above the ischial arch, tli])s under the bulbo-cavernosus muscle, and ramifies in 

 the corpus spongiosum. 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. 



(4a) 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 the internal pudic nerve, supplies the clitoris, and gives twigs to the 

 vulva. 



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



Fig. 454. — Cross-sectiox of Tail of Horse. 

 1, Dorso-lateral coccygeal ve.<.sel.s ami nerve; 2, ventro-lateral coccygeal artery and nerve; 3, middle 

 coccygeal artery; 4. sacro-coccygeu.s superior; 4' , sacro-coccygeus lateralis; o, 6' , intertransversales; 6, sacro- 

 coccygeus inferior; 7 , recto-coccygeus; 8, coccygeal fascia; 9, fibro-cartilage between fourth and fifth coccygeal 

 vertebra;. The veins are black. 



articulation (Fig. 451). It passes backward under the wing of the sacrum, then 

 along the pelvic surface of the bone below the inferior 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 for- 

 amen between the last lumbar vertebra and the sacrum and through the ventral 

 sacral foramina. They give off branches to the spinal cord and its membranes 

 which reinforce the ventral spinal artery, and others which emerge through the 

 dorsal sacral foramina and supply the muscles and skin of the croup. 



(2) The middle coccygeal artery (A. coccygea) is an unpaired vessel which 

 arises from the right or left lateral sacral or from a lateral coccygeal artery. It 

 passes backward on the pelvic surface of the sacrum to the median line and con- 

 tinues in that position along the tail betAveen the depressor muscles, supplj'ing 

 these and the skin. 



(3) The posterior gluteal or ischiatic artery (A. glutea caudalis) emerges 



