THE CIRCULATORY APPARATUS OF BIRDS. 735 



question : so tliat when tbe latter contracts at the systole, it is applied ajj^ainst 

 this septum and closes the passage."" ^ 



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

 of which are likewise thicker than those of the right. 



The auricles have a kind of diverticulum or sinus, where 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 

 middle line towards the anterior extremity of the kidneys, and in this situation 

 it reaches the sacral vertebr;«, 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 hrachio-cephaUr (or mnominate) 

 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, the volume of which 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 Rarkow 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-cepha'ic 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 spring 

 from a corresponding brachial trunk ; and, placed at first on the sides of the neck, 

 they make a curve, with convexity anterior, and gain the middle 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 cobHuc trunk, which commences at the middle of the 

 lower face of the lung, and, descending 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 pancreafieO' 

 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 dis 

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

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

 intestine. 4. The spermatic or ovarian arteries. The inferior or posterior mesen- 



' Milne-Edwards, Leforn sur la Physiologic et VAnatomie Comparee de VHomme et de$ 

 Animaux, vol. iii. 



