THE POSTERton AORTA. 5Zl 



postiiior. The fir»t, destined for the-Bmall intestine, creeps above it, between the two 

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

 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 

 curvuture of the cjecum, and anastomoses by an arch with the terminal extremity of the 

 parent-branch of the arteries supplying the small intestine. 



Small mesenteric artery. — Very short and narrow. 



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

 disposition from the analogous vessels in Solipeds. 



2. Posterior Aorta in the Fig. 



"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 

 justiiiable, 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 psoas muscle, and traverses the abdominal wall in the 

 vicinitv of the transverse processes of the lumbar vertebrse. We will ijpeak presently of 

 the middle sacral. 



B. Visceral Bkanches. — ^I have not found in the Dog any special hronchial arteries ; 

 but there are four or five (esophageal 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 cceliac trunk is again divided into three branches, whose disposition is as follows : 

 The gastric, or stomachic coronary artery, does not divide into two branches fanterior 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. u j t ■ 



The splenic artery reaches the spleen at tlie 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 hepatie 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 panereatico-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 cceliac artery ; it tonus a curve 

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

 duodenal branch of tlie hepatic. From its convexity are detach, d several filaments 

 (filaments to the small intestine), that form arches towards the sn.aller curvature ot that 

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

 and branches to the colon ; the latter are sometimes large. -,■,..,• ^ 



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

 two branches . one passing forward, and the other backward ; they form the hajmorrhoidal 

 vessels (see Fig. 209). , . . ■ 



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



