CIRCULATING AND RESPIRATORY APPARATUS. 



385 



three large branches ; of which the two first subdivide into the 

 trunks that convey the blood to the head (the carotid arteries), 

 to the wings (the sulclavian), and to the muscles of the chest 

 (the mammary ^ which are of large size in Birds, on account of 

 the great development of those muscles, whose office is to draw 

 down the wings) ; whilst the third curves downwards around 

 the right bronchus, and constitutes the descending aorta. There 

 are some peculiarities in the mode of distribution of the arteries ; 

 but they are not important, and it is only to be remarked, that 

 in different points of the body they constitute remarkable plexuses, 

 by frequently anastomosing together. The venous system ter- 

 minates in three large trunks ; one of which is analogous to the 

 Vena Cava of the Mammalia; and the two other nearly corre- 

 spond with the two subclavian veins, which do not unite to form 

 a common trunk (or superior vena cava), as in these last 

 animals. 



348. The apparatus of Respiration presents more remarkable 

 peculiarities than that of circulation. The lungs, as we have 



Trachea 



Pulmonary vessels 



Lun 

 Bronchial orifices. 



-Bronchial tube 

 opened. 



Bronchial tube 

 opened. 



TIG. 203. LUNGS OF BIRDS. 



already said, communicate with large cells hollowed in the cellu- 

 lar tissue, and thus transmit the air into all parts of the body 

 (Fig. 203) ; so that the respiration may be regarded as double, 



