THE INTERNAL ILIAC ARTERIES. 541 



it ends in two branches : the ischiatic and lateral coccygeal arteries, to which 

 must be added the middle coccygeal artery, usually emitted by the subsacral 

 vessel of the right side. 



Collateral Branches.— The lateral sacral artery distributes on its 

 course several insignificant ramuscules destined for the neighbouring parts, 

 and four spinal branches which enter the vertebral canal by the inferior 

 sacral foramina, and leave it again by the superior, after throwing off some 

 divisions to the posterior extremity of the spinal cord and the nerves of 

 the tail ; these branches ramify in the muscles lying on the sacral spine. 



Terminal Branches. — 1. Ischiatic Artery. — It crosses the ligament of 

 the same name to place itself under the superior extremity of the anterior 

 portion of the long vastus, passes backwards and downwards, and divides 

 into several branches which descend into the ^bsfcance of the ischio-tibial 

 muscles (semimembranosis and semitendinosis), to beneath the ischial 

 tuberosity. These branches anastomose, by their extremities, with the 

 ascending branches from the the femoro-popliteal as well as with the 

 divisions of the obturator and deep femoral arteries. 



2. Lateral Cocovgeal Artery. — This vessel represents the continua- 

 tion of the lateral sacral artery, though not by its volume, which is much 

 less than the ischiatic artery, but in its direction. It proceeds from before 

 to behind, for the whole length of the coccyx, between the rudimentary 

 vertebrse of that region and the depressor muscles of the tail, gradually 

 diminishing in volume, and detaching on its course a series of collateral 

 ramuscules which are expended in the muscles and integuments of the tail. 



There has been described a superior lateral artery, a branch of the pre- 

 ceding, and which passes between the elevator muscle of the tail and the 

 superior face of the coccygeal vertebrae ; but this artery never exists : the 

 superior coccygeal muscle receives its blood by branches analogous to the 

 spinal branches of the intercostal, lumbar, and sacral arteries, and which 

 emanate from the lateral coccygeal artery at each of the vertebral bodies.; 



3. Middle Coccygeal Artery. — The origin of this vessel is liable to 

 numerous variations. Ordinarily, it is detached from the right subsacral 

 artery, in common with the lateral coccygeal of the same side. At other 

 times, it escapes from the lateral at 5 or 6 inches from its origin. In a 

 specimen now before us, it arises nearly from the middle of the subsacral 

 artery. And it may also proceed from either the left sacral or the corres- 

 ponding lateral coccygeal artery. 



Whatever may be its point of emergence, this vessel is placed heneath the in- 

 ferior face of the caudal vertebrae, between the two depressor muscles of the tail, 

 crosses t'-e suspensory ligament of the rectum, and extends to the extremity 

 of the ciccyx, distributing ramuscules to right and left, and even below. 



4. Ilio-muscular or llio-lumbar Artery. (Figs. 375, 14 ; 277, 8.) 

 Immediately after clearing the inferior face of the lateral angle of the 

 sacrum, and even often before, the pelvic trunk gives off from its external 

 side, and at a right angle, the ilio-lumbar artery, which passes directly 

 outwards, behind the sacro-iliac articulation, between the iliacus muscle and 

 the bony surface covered by it, and emits divisions that proceed to the 

 above-named articulation, as well as to the muscles of the sublumbar 

 region. Near the angle of the haunch, it terminates in several branches, 

 which bend upwards on the external border of the ilium, to penetrate the 

 principal gluteal muscle, or the muscle of the fascia lata (tensor vagin© 

 femoris.) 



