202 CIRCULATORY SYSTEM. 



natino- branches. It famishes — 1. Sacru-spinal hnnuhes, five or 

 six in number, which enter the spinal canal through the internal 

 sacral foramina. 2. The peroneal artery, a branch as large as, 

 or even larger than, the trunk itself, of which it might be more 

 correctly, perhaps, considered as the continuation; and which soon 

 divides into several ramifications, of which — a. many run to the 

 gluteal muscles ; h. while others descend upon the back of the 

 thigh ; c. and a third set are distributed to the an.d muscles, and 

 to the skin and cellular substance of the perineum. 3. The 

 lateral cocci/geal artery, one of the terminating branches of the la- 

 teral sacrai, runs close to the side of the os coccygis, even to its 

 extreme point, preserving the line of direction of the spine, 

 diminishing in diameter as it recedes, and distributino; numerous 

 branches laterally to the coccygeal muscles. 4. The inferior 

 coccygeal artery, rather larger than the lateral, takes the same 

 correlative course along the inferior and lateral part of the bone, 

 and may also be traced to the tip. It sends down a long slender 

 twig or two to the anus: the remainder of its branches are dis- 

 tributed to the coccygeal muscles. 



The middle sacral artery is a very inconsiderable 

 branch coming ofl', generally, from the trunk of the posterior aorta 

 at its angle of bifurcation into the internal iliacs. It is traceable 

 for a little way only, along the middle of the sacrum. 



The External Iliac Arteries, 



Right and left, result from (what may be significantly described 

 as) ihejirst bifurcation of the posterior aorta ; which takes place 

 underneath the body of the last of the lumbar vertebrae. They 

 take the same oblique direction (outward and backward) as the 

 internal iliac ; but they are less in diameter, and bear no compari- 

 son in respect to length. The best guide to their situation is the 

 brim of the pelvis: considering the bowels to be removed, they 

 are found running along this brink of the cavity, uncovered by 

 any thing but peritoneum, following the bony curvature outward 

 to their termination ; which takes place upon the same brim, 

 about midway between the symphysis pubis and anterior spinous 

 process of the pelvis. Each vessel gives off — 



1. The circumflex artery of the ileum : a large 

 branch that departs from the outward side of the trunk, near its 

 origin. It winds directly across the loins to the flank, covered 

 only by peritoneum, crossing in its way the two psoae and the 

 iliacus ; arriving in front of the anterior spinous process of the os 

 innominatum, it splits into two vessels, which take opposite 

 comses : one inclines backward, penetrating the transversalis, to 

 which and to the originating portion of the internal obliqiie muscle 



