THE INTEhNAL ILIAC ARTERIES. 623 



two pillars of that rtrascle. In the abdominal cavity, close to the anterior mesenteric, the aorta 

 gives ciff a branch that soon divides into two: one is diaphragmatic, and descends on the 

 ])Oaterior face ot that muscle; the other reaches the sublumbar region, passes over the psoas 

 muscle, and traverses the abdominal wall in the vicinity of the transverse processes of the 

 lumbar vertebrje. 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 oisophageal arteries that arise from different points of the tlioracic 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 coeliac axis is again divided into three branches, 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 spreail 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-oraental artery. On the duodenum, the 

 latter gives origin to the pyloric and the pancreatico- duodenal branches ; the latter is volu- 

 minous, is lodged in the substance of the pancreas, and anastomoses by its last filaments with 

 the anterior mesenteric. 



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

 with the convexity 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 posterior mesenteric commences near the termination of the aorta, and divides into two 

 branches— one passing forward, the other backward; they form the hsemorrboidal vessels 

 (see Fig. 290). 



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



Comparison of the Aoeta of Man with that of Animals. 



The aorta in Man offers the same general arrangement as in the Carnivora, the trunk 

 being inflected across, to be placed along the body of the dorsal and first lumbar vertebrai, 

 where it terminates in the iliac vessels. 



It furnishes the coronary arteries, the arteries of the head and thoracic limbs — which will 

 be noticed hereafter ; ami the parietal and visceral branches to the chest and abdomen. At 

 first these are the intercostals, beyond the third space ; the diaphragmatic arteries, superior 

 and inferior according as they occupy one or other face of the diaphragm ; and, lastly, the 

 lumbar arteries. 



Among the visceral branches are distinguished : 1. The bronchial arteries, two in number; 

 the left arises from the concavity of the aortic arch, and enters the lungs with the left bronchus ; 

 the right originates alone or in common with the preceding, and enters on the right bronchus. 

 2. The oesophageal arteries, disposed somewhat as in the Dog. 3. The coeliac trunk, tlie 

 distribution of which is nearly identical with tlmt of the Carnivora. 4. The superior or great 

 mesenteric, disposed in arches as in the Dog (see Fig. 292, 9). Its last branches pass to the caecum, 

 and the ascending and origin of the transverse portion of the colon. 5. The inferior or small 

 mesenteric, which arises from 1| to 2 inches from the bifurcation of the aorta ; this artery descends 

 into the meso-colon, and terminates on the sides of the rectum by the haemorrhoidal vessels ; 

 to the left, they emit branches to the large intestine ; the first ascend along the descending 

 colon, and anastomose on the transverse colon with the right colic brancli of the superior 

 mesenteric. 6. The renal and capsular arteries, which do not offer important differences. 7. 

 Lastly, the spermatic arteries, which are remarkable for the length of their course, commencing, 

 as they do, at the aorta, a short distance below the renal vessels. 



Article IIL^-Internal Iliac Arteries, or Pelvic Trunks 

 (Figs. 338, 368, 370). 



The two internal iliac arteries represent the middle or internal branches of 

 the quadrifurcatiou formed by the posterior aorta at its terminal extremity. 



