648 THE CIRCULATORY APPARATUS OF BIRDS. 



and the cervical reservoir. In the domesticated species, it has the form of an acute cone, 

 whose base is surmounted by a less distinct auricular mass than in the Mammalia. 



Internally it has four cavities. The right ventricle is more crescent-shaped than in 

 Solipeds, and in a manner envelops the left ventricle in frunt and to the right ; it does 

 not reach the point of the heart. The auricular valve is not tricuspid, and offers a very 

 remarkable arrangement. " This valve, in fact, instead of being formed as usual by 

 membranous curtains whose margin is retained by cords fixed to the walls of the 

 ventricles, is composed of a wide muscular leaf which appears to be a portion of the 

 inner wall of the ventricle detached from the interventricular septum. This septum is 

 convex, and the auriculo-ventricular orifice is situated in the space comprised between it 

 and the muscular valve in question ; so that when the latter contracts at the systole, it is 

 applied against this septum and closes the passage." l 



There is nothing particular to note with regard to the left ventricle, whose walls 

 are likewise thicker than those of the right. 



The auricles have a kind of diverticulum or sinus, in which the veins that open into 

 each of these cavities unite. 



ARTICLE II. THE ARTERIES. 



The aorta of Gallinaceous birds ascends beneath the lower face of the right lung, then 

 turns abruptly backwards and a little to the left. It attains the median line towards 

 the anterior extremity of the kidneys, and in this situation it reaches the sacral vertebrae, 

 where it divides into three branches the arteries of the pelvic limbs, and the middle 

 sacral artery. 



Close to its origin, the aorta gives off the brachio-cephalic {or innominate) trunks. 

 With the Fowl this name is perfectly correct, as they both furnish vessels to the wings 

 and head. The right passes upwards and forwards, is inflected backwards at the first 

 rib, and continued on the lower face of the wing by the humeral artery. It throws off a 

 thoracic artery, whose volume is in relation with that of the pectoral muscles ; this artery 

 emits superficial branches that form in the skin of the abdomen, with other vessels, a 

 very rich plexus named by Barkow the rete mirabile of incubation. It afterwards gives off 

 a cephalic trunk, from which arise the ascending cervical, vertebral, and right carotid 

 artery. The left brachio-cephalic trunk has the same distribution as the right, a slight 

 difference only being observed in its direction ; on leaving the thoracic cavity it describes 

 a small S curvature. 



The carotid arteries exhibit a somewhat curious arrangement. Each springs from 

 a corresponding brachial trunk ; and placed at first on the sides of the neck they make 

 a curve, whose convexity is anterior, and. gain the median line by passing, the right 

 above the oesophagus, the left above the trachea. They remain beside each other, 

 beneath the longus colli, from the second last to the second cervical vertebrae, where 

 they separate at an acute angle and reach the border of the jaw, terminating there in 

 two branches the internal and external carotid arteries. 



The other collateral branches furnished by it, are : 1, The intercostal arteries. These 

 may arise from the subcostal branches which are parallel to the aorta ; thus, in the Fowl, 

 there is a common descending intercostal which proceeds from the vertebral, and a common 

 ascending intercostal that leaves the aorta as it passes into the abdomen ; 2, The 

 ccdiac trunk, which commences at the middle of the lower face of the lung, and descend- 

 ing obliquely backward, reaches the posterior aspect of the liver. It divides into several 

 ramuscules, of which there are three principal vessels: a very fine one goes to the 

 spleen ; a left or middle one passes to the gizzard along the proventriculus ; the third, 

 more voluminous, is directed to the right side, gives a twig to the liver, and is continued 

 by a long pancreatico-duodenal branch that joins the extremity of the loop which the 

 intestine forms at its origin ; 3, The anterior or superior mesenteric, which arises at a short 

 distance behind the coeliac trunk, enters the mesentery, and is directed backwards, 

 describing a curve whose convexity is antero-inferior, and which emits twigs to the 

 intestine ; 4, The spermatic or ovarian arteries. The inferior or posterior mesenteric 

 leaves the subsacral artery, and, by some ramuscules, reaches the rectum and cloaca. ' 



Shortly before its termination in three branches, the aorta gives off an artery that 

 crosses the middle portion of the kidneys, leaves the abdominal cavity, and becomes dis- 

 tributed to the anterior muscles of the thigh, after detaching the epigastric artery. The 

 latter proceeds forward, beneath the skin of the abdomen, and anastomoses with the 

 ramifications of the thoracic artery. 



1 Milne Edwards ' LeQons sur la Physiologic et 1'Anatomie Comparee de 1'Hommo 

 et des Animaux.' Vol. iii. 



