THE POSTERIOR AORTA. 537 



posterior. The first, destined for the small intestine, creeps above it, between the two 

 layers of the mesentery, and passes backward by describing a curve which gives off from 

 its convexity that is, below, a great number of branches, analogous in their mode of 

 termination to the arteries of the small intestine in the Horse. The posterior branch goes 

 to the large intestine, where it separates into two principal branches : one which passes 

 to the colon, and whose divisions cross to the right, from before to behind and from above 

 to below, the convolutions described by that viscus ; another which reaches the concave 

 curvature of the caecum, and anastomoses by an arch with the terminal extremity of the 

 parent-branch of the arteries supplying the jsrnall intestine. 



Small mesenteric artery. Very short and narrow. 



Renal, spermatic, and small testicular arteries. These do not differ in their essential 

 disposition from the analogous vessels in Solipeds. 



2. Posterior Aorta in the Pig. 



With the exception of the mesenteric vessels, whose distribution resembles that 

 already indicated for Ruminants, and with the exception, also, of the middle sacral artery, 

 which will be alluded to when describing the internal iliac arteries, all the branches 

 given off by the posterior aorta comport themselves almost as in the Horse. 



3. Posterior Aorta in Carnivora. 



In these animals, as well as in the Pig, the denomination of posterior aorta is not 

 justifiable, because the arteries of the head and thoracic limbs spring directly from the 

 aortic arch. 



The branches of the aorta are distinguished as parietal and visceral. 



A. PARIETAL BRANCHES. Beyond the fourth space, the intercostal arteries are fur- 

 nished by the aorta the first is voluminous, and throws off some considerable filaments 

 to the muscles of the withers. The first two lumbar arteries arise from the thoracic 

 portion of the aorta, because of the very backward insertion of the diaphragm ; the third 

 is detached between the two pillars of that partition. In the abdominal cavity, close to 

 the great mesenteric, the aorta gives off a branch that soon divides into two : one is 

 diaphragmatic, and descends on the posterior face of that muscle ; the other reaches the 

 sublumbar region, passes over the pisoas muscle, and traverses the abdominal wall in the 

 vicinity of the transverse processes of the lumbar vertebrae. We will speak presently of 

 the middle sacral. 



B. VISCERAL BRANCHES. I have not found in the Dog any special bronchial arteries ; 

 but there are four or five ossophageal arteries that arise from different points of the 

 thoracic aorta ; they descend into the mediastinum, to the right and left of the 

 oesophagus, to which they are distributed. They furnish branches that accompany the 

 bronchi and enter the lungs. 



The cosliac trunk is again divided into three branches, whose disposition is as follows : 

 The gastric, or stomachic coronary artery, does not divide into two branches ('anterior and 

 posterior gastric) as in Solipeds. Near its origin it furnishes a pancreatic branch ; then 

 it expends itself in a great number of filaments that are spread over the posterior face 

 and great tuberosity of the stomach, or over its anterior face after crossing the small 

 curvature. 



The splenic artery reaches the spleen at the middle of its upper border. It gives on 

 its course : 1, A splenic branch that enters the upper extremity of that organ ; 2, The 

 left gastro-omental. The hepatic artery provides the principal hepatic vessel at the 

 posterior fissure of the liver ; it is then continued by the right gastro-omental artery. 

 On the duodenum, the latter gives origin to the pyloric and the pancreatico-duodenal 

 branches; the latter is voluminous, is lodged in the substance of the pancreas, and 

 anastomoses by its last filaments with the great mesenteric. 



The great mesenteric artery arises in the vicinity of the coeliac artery ; it forms a curve 

 whose convexity is backward, and anastomoses by its extremity with the pancreatico- 

 duodenal branch of the hepatic. From its convexity are detached several filaments 

 (filaments to the small intestine), that form arches towards the smaller curvature of that 

 viscus. Behind, and at a short distance from its origin, it gives a branch to the caecum 

 and branches to the colon ; the latter are sometimes large. 



The small mesenteric commences near the termination of the aorta, and divides into 

 two brandies . one passing forward, and the other backward ; they form the haamorrhoidal 

 vessels (see Pig. 209). 



There is nothing special to note with regard to the renal and spermatic arteries. 



