218 



THE VITAL FUNCTIONS. 



357 H 



trunk, wliich is the ascending aorta. This aorta 



soon divides into two trunks, 

 which, after sending branches 

 to the head and neck, bend 

 downwards (as is seen at o, p), 

 and unite to form a single trunk 

 (a), which is the descending 

 aorta. From this vessel proceed 

 all the arteries which are dis- 

 tributed to the trunk and to 

 the limbs, and wliich are repre- 

 sented as situated at b: these 

 arterial ramifications are con- 

 tinued into the great venous 

 trunks, which, as usual, constitute the venae cavae 

 (c), and terminate in the auricle (d). 



From each of the trunks which arise from the 

 primary division of the aorta, there proceed the 

 small arteries (l), which are distributed to the lungs 

 (g, h), and convey to those organs a part only of 

 the mass of circulating blood. To these pulmonary 

 arteries there correspond a set of veins, uniting in 

 the trunks (i), which bring back the aerated blood 

 to the right cavity of the auricle of the heart (d), 

 which pours it into the ventricle (e), where it is 

 mixed with the blood which has returned by the 

 venee cavae (c), from the general circulation. Thus 

 the blood is only partially aerated ; in consequence 



Dr. Davy ; and that he has discovered that the Siren has also a 

 distinct pulmonic auricle; whence he infers that wherever lungs are 

 sufficiently developed to effect a change in the blood, that fluid is 

 conveyed to the ventricle by a distinct route, and the pulmonary 

 veins thus defended from the pressure of the blood accumulated in 

 the right auricle. 



