TEE POSTERIOR AORTA. 617 



B. Arteeies of the Right Fasciculus. — The right fascicuhis of the great 

 mesenteric artery constitutes, at first, a single trunk some inches in length, which 

 soon divides into four branches. These are as follows : the ileo-ccecal artery, the 

 two ccecal arteries, and the right or direct colic artery. 



Ileo-Caecal Artery (Fig. 283, 3). — This vessel often has its origin from 

 the internal csecal artery. It is placed between the two layers of the mesentery, 

 follows for a short distance, and in a retrograde manner, the ileo-csecal portion 

 of the small intestine, and wholly anastomoses with the last artery of the left 

 fasciculus, after emitting a series of branches, which are distributed to the 

 intestinal membranes. 



Caecal Arteries. — Distinguished into internal or superior, and external or 

 inferior, these two arteries pass downward and a httle to the right, towards the 

 concavity of the caecal flexure, embracing between them the terminal extremity 

 of the small intestine, and lying at the middle part of the csecal sac, following 

 its direction. 



The superior, or internal ccecal artery, is lodged in the most anterior of the 

 fissm-es formed by the longitudinal bands of the cscum, and extends beneath 

 the serous tunic to nearly the point of the viscus, where it terminates by 

 anastomosing with the external caBcal artery. The branches furnished by this 

 artery during its course escape in a perpendicular direction, and distribute their 

 ramifications on the walls of the caecum (Fig, 283, 4), 



The external, or inferior ccecal artery, passes between the csecum and the origin 

 of the colon, to descend along the first-named organ by placing itself in one of 

 the external fissures, which is situated outwardly and posteriorly. Arriving at 

 the point of the organ, this artery bends over it to anastomose with the vessel 

 just described (Fig. 283, 7). It gives off on its track a series of transverse 

 ramifications, similar to those of the latter artery ; and besides these, a remarkable 

 branch which may be named the artery of the ccecal arch. This branch is detached 

 from the principal vessel near the origin of the colon, and ascends to the caecal 

 arch, following its concavity outwardly to pass forwards and downwards to the 

 first portion of the large colon, where it disappears after following a certain 

 com'se. The nimierous collateral branches detached by this artery are sent to 

 the walls of the latter portion of intestine, and the arch of the caecum 

 (Fig. 283, 6). 



Right or Direct Colic Artery (Fig. 283, 7). — This is the largest of the 

 branches composing the right fasciculus of the anterior mesenteric artery. 

 Destined for the right portion of the flexure fonned by the large colon, it lies 

 immediately beside that viscus, beneath the peritoneal membrane, following it 

 from its origin to its pelvic flexure, where the artery anastomoses by inosculation 

 with the left colic or retrograde artery. 



C. Arteries of the Ajstterior Fasciculus. — These are only two in 

 number : the left colic or retrograde, and the ^rs^ artery of the small colon, joined 

 at their origin to an extremely short trunk. 



Left Colic or Retrograde Artery (Fig. 283, 8). — This is carried to the 

 left portion of the colic flexure, which it passes over, beneath the peritoneum, 

 from the terminal extremity of the viscus to the pelvic flexure, where it meets 

 the right artery ; in this manner it follows a course the inverse of that pursued 

 by the food, whence its name of retrograde colic artery. 



Considered collectively, the two colic arteries represent a loop or flexure exactly 

 like that formed by the large colon itself. They proceed parallel to each other 



