EEPORT ON THE SPHENISCIDiE. 141 



The Aorta. 



The aorta of Eudyptes chrysocome (PI. XT. fig. 1), after leaving the left ventricle, 

 appears at the base of the heart lying to the right of the inter-auricular sulcus. It then 

 arches as usual over the right bronchus, and continues along the lower surface of the 

 vertebral column as far as the last lumbo-sacral vertebra, where it terminates by dividing 

 into three branches, to be afterwards described. In this course it rests against the 

 right side of the large hypapophyses of the dorsal region. Below the artery are the 

 root of the right lung, the liver, and the coils of the small intestine. 



The aorta gives off the following branches. 



I. — The Innominate Arteries. 



These pass off from the summit of the aortic arch, on either side of the middle line. 

 They extend obliquely forwards and outwards, and terminate by dividing into the common 

 carotid and subclavian arteries. In the fork formed liy the innominate arteries lie the 

 trachea and oesophagus. 



(1.) The Subclavian Artery. 



In Eudyptes chrysocome this artery does not exceed ^th of an inch in length. It 

 extends from its origin obliquely outwards and forwards, and arching over the apex of 

 the lung terminates under cover of the coracoid bone, by dividing into the thoracic and 

 brachial arteries. Prior to its termination the subclavian artery gives off two branches, 

 which may be named the middle pectoral and the internal mammary arteries. 



The Middle Pectoral Artery comes off from the subclavian immediately before its 

 termination. It passes directly downwards, pierces the coraco-brachiaUs muscle, and 

 comes into relation with the inner border of the coracoid bone. Here it passes through 

 a foramen, bounded on the outer side by the coracoid bone, and on the inner side by a 

 ligamentous band, which is attached to that bone. After passing through this foramen 

 along with the accompanying vein, the artery enters the substance of the pectorahs 

 medius muscle, which it suj^j^lies. 



The Internal Mammary Artery arises from the subclavian close to the termination 

 of the latter. It passes horizontally backwards within the cavity of the thorax, and 

 applying itself to the margin of the sternum, extends for some distance along that bone. 

 It terminates by breaking up into branches for the supply of the triangularis sterni, 

 and sternal intercostal muscles. 



The Thoracic Artery. — This, which is the larger of the two terminal branches of the 

 subclavian passes outwards, lying between the pectoralis minor below and the serratus 

 anticus minor above. It divides almost at once into three or four branches, which again 



