246 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



Arteries. A single aortic arch is present, the aorta, the first 

 part of which (arch of aorta) curves round to the right, giving 

 off branches which supply the head, neck, wings, and pectoral 

 muscles, and then, reaching the middle dorsal line, becomes the 

 dorsal aorta. This runs straight to the tail, where it becomes the 

 caudal artery, giving off branches on its way to the viscera, hind- 

 limbs, and body-wall. 



From the arch of the aorta, large right and left innominate arteries are 

 given off close to the heart, after which the calibre of the aorta diminishes 

 considerably. Each innominate divides very quickly into common carotid 

 and subclavian arteries. The common carotid runs along the neck, soon 

 giving off the vertebral arteri/ (which supplies the brain and spinal cord, 

 and occupies the vertebrarterial canal), and, at the angle of the jaw, 

 divides into internal and external carotids. The former supplies the brain, 

 the latter the head generally. The subclavian divides almost at once into 

 the small brachial and large pectoral arteries, which respectively supply the 

 wing and muscles of the chest. The dorsal aorta gives off an unpaired 

 cceliac artery, the branches of which run to the proventriculus, gizzard, 

 spleen, duodenum, pancreas, and last loop of the small intestine; while, 

 slightly behind this, an unpaired anterior mesenteric artery comes off, which 

 supplies the rest of the small intestine. Still further back the small 

 anterior renal arteries, for the anterior kidney-lobes ; the femoral arteries, 

 for the extensor muscles of the thigh ; and the sciatic arteries, for the flexor 

 muscles of the thigh and for the rest of the hind-limb, are given off in suc- 

 cession. Branches of the sciatic, the middle and posterior renal arteries, 

 supply the corresponding kidney-lobes. Just behind the kidneys the dorsal 

 aorta gives off an unpaired posterior mesenteric artery to the large intestine 

 and cloaca, and paired internal iliac arteries to the hinder part of the pelvis, 

 and then runs, as the caudal artery, into the tail. 



The pulmonary artery arises from the right ventricle, and soon 

 divides into right and left branches for the right and left lungs. 



Veins. These may be dealt with under the headings of caval 

 system, hepatic portal system, and pulmonary veins. 



(1) Caval System. There are two precavals (superior venae 

 cavse) and a postcaval (posterior vena cava), all opening into the 

 right auricle. Each precaval is a large, short vein, formed by 

 the union of three trunks jugular, brachial, and pectoral, return- 

 ing the blood from one side of head and neck, one wing, and 

 chest-muscles of one side, respectively. 



The jugular runs back from the base of the head (where it is united by 

 a cross-trunk with its fellow), along one side of the neck, and not far from 

 its union with the other two trunks, receives the vertebral vein. 



The postcaval is a large vein returning the blood from the 

 posterior part of the body, formed just in front of the kidneys, 



