THE POSTERIOR AORTA. 531 



Such is the general arrangement of the arteries of the small intestine ; 

 and it remains to indicate some of their special characters, which are as 

 follows : 1, The longest arteries of the small intestine are the most posterior, 

 as they follow the development of the mesentery, by which they are sus- 

 tained ; 2, The anterior arteries generally form two series of superposed 

 arches, before sending their divisions to the intestine ; 3, The first reaches 

 the duodenum and anastomoses with the duodenal artery a branch given off 

 by the coeliac axis ; 4, The last communicates with the ileo-caecal artery one 

 of the branches of the right fasciculus. 



B. ARTERIES OF THE EIGHT FASCICULUS. The right fasciculus 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-C^ECAL ARTERY (Fig. 271, 3). This vessel often has its origin 

 from the internal cascal artery. It is placed between the two layers of the 

 iresentery, follows for a short distance, and in a retrogade manner, the ileo- 

 caecal 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 little to the right, 

 towards the concavity of the ca3cal flexure, embracing between them the 

 terminal extremity of the small intestine, and lying at the middle part 

 of the caecal sac, whose direction they follow. 



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

 of the fissures formed by the longitudinal bands of the caecum, and extends 

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

 by anastomosing with the external caecal 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. 271, 4). 



The external, or inferior caecal artery, passes between the caecum and the 

 origin of the colon, to descend along the first-named receptable 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. 271, 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 caical arch. This branch is detached from the principal vessel near the 

 origin of the colon, and ascends to the caecal arch, whose concavity it follows 

 outwardly to pass forwards and downwards to the initial portion of the large 

 colon, where it disappears after following a certain course. The numerous 

 collateral branches detached by this artery are sent to the walls of the latter 

 portion of intestine, and the arch of the ca3cum (Fig. 271, 6). 



RIGHT OB DIRECT COLIC ARTERY (Fig. 271, 7). This is the largest of 

 the branches composing the right fasciculus of the great mesenteric artery. 

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

 lies immediately beside that viscus, beneath the peritoneal membrane, 

 following it from its origin to its pelvic curvature, where the artery 

 -lastomoses by inosculation with the left colic or retrograde artery. 



C. ARTERIES OF THE ANTERIOR FASCICULUS. These are only two in 

 lumber : the left colic or retrograde, and the first artery of the small colon, 

 )ined at their origin to an extremely short trunk. 



LEFT COLIC OR RETROGRADE ARTERY (Fig. 271, 8). This is carried 



