62 COMPAEATIVE ANATOMY. 



auricle, thence is conveyed to the left ventricle, to be sent to 

 the head and upper extremities by the right or ascending 

 aorta. But the lower portion of left aorta does not contain 

 pure venous blood, since it receives blood from the right 

 aorta through -a communicating branch (ductus Botalli). Nor 

 does the right aorta at all times contain pure arterial blood, 

 for it may receive venous blood from the right ventricle 

 through an opening in the inter-aortic septum. Lung is 

 coarsely cellulated ; sometimes single. Mechanism of respi- 

 ration in Chelonia by the muscles of flank spaces (inspira- 

 tory) and muscles within breast box (expiratory) ; in Ophidia 

 by movement of x the ribs. Red blood corpuscles large, gen- 

 erally oval, nucleated. Portal circulation receives blood from 

 kidneys, posterior extremities, and tail. 



Aves. Heart of four cavities. Circulation as in man, ex- 

 cepting that the aorta turns to the right. Lungs fixed, double ; 

 bronchi communicate with cavities of bones extensively in 

 Rhamphastos (toucan); slightly in Gallus (fowl); but not at 

 all in Hirundo (swallow). Mechanism of respiration resident 

 in abdominal muscles since ribs and sternum remain fixed. 

 Rudiment of a diaphragm in Psittacus (parrot). Respiration 

 of egg of reptile and bird through allantois. 



Mammalia. Heart of four cavities ; plan of circulation as 

 in man. In Halicore (dugong) there is a double apex to 

 heart one for each ventricle. Bone exists in ventricular 

 septum in ox. Foramen ovale at times persistent, as in 

 Phoca (seal). Several methods of origin of the great arte- 

 rial trunks from aorta. With the ruminants a single trunk 

 from the arch divides into the subclavian and carotids ; with 

 the carnivores, the innominate artery gives both carotids as 

 well as right subclavian. Anomalous arrangements of these 

 vessels in man are reproductions of the normal ones of the 

 lower mammals. Curious anastomoses of vessels (wonder 

 nets) seen in Bradypus (sloth) and Cetacea. 



The general plan of the circulation in Yertebrata can be 

 detected in the development of the blood-vessel system in 

 man. Thus in the human foetus, the five cervical arches rep- 

 resent the five branchial arches of the fish. In the former, 



