14 



THE FUR SEALS OF THE PRIBILOF ISLANDS. 



al- 



Tbe rigbt muscle runs forward about twice the distance of the inner, and divides into 

 an outer and an inner branch. The latter becomes lost upon the ventral wall of the 

 ventricle, while the other bears six chord;e tendina\ The third papillary muscle is 

 very short. It projects forward and to the right, into the cavity of the ventricle, from 

 the septum near its ventral border, just back of the right auriculoveutricular valve. 

 The pulmonary vessels. — The ductus BotaUi persists throughout life as a hollow 



vessel, closed at each end by a membrane. It 

 is proportionately larger in a pup than in an 

 old animal, but eveu in tlie latter it is well 

 developed. 



There are four pulmonary reins. On the left 

 side one large one comes from the anterior lobe 

 of the coriespondiug lung and enters the left 

 auricle at its anterior left aspect. From the 

 posterior lobe on the same side three veins, 

 decreasing in size from before backward, con- 

 verge toward the posterior outer aspect of the 

 left auricle and unite near it, forming a single 

 trunk less than half an inch long. On the 

 right side a very large trunk comes from the 

 most posterior lobe of the right lung and is 

 joined by a smaller vein from the middle lobe. 

 The common trunk thus formed is very short, 

 resembling the one on the left. These two 

 empty very close together into the posterior 

 part of the left auricle. The anterior vein on 

 the right side is formed by the union of numer- 

 ous branches from the anterior and middle 

 lobes of the lung, of which branches the most 

 posterior is the largest, and goes bac^kward 

 and inward doivsad to the right auricle and 

 base of anterior vena cava, to the anterior 

 right aspect of the left auricle. 



The systemic arteries. — The aortic arcli gives 

 off two main trunks, the brachiocephalic and 

 left subclavian. The brachiocephalic is very 

 short and gives oft" close together, first the left 

 common carotid and then the right coinnton 

 carotid. Tlieremaiiider of the trunk continues 

 outward and forward as the ri(/ht subclavian. 

 Where tlie latter leaves tlie thoracic cavity it 

 gives oft' three i)rincii)al trunks, the internal 

 mammary, the vertebral, and the thyroid axis. 



The internal mammary runs inward and backward along the dorsal side of the 

 costal cartilages just external to the sternum. 



The vertebral artery arises from the subclavian a little internal to tlie origin of 

 the internal mammary. It runs forward and inward, entering the canal of the verte- 



FlG. 3. — Posterior arterial system. 

 ab. a. Abdominal aorta. 

 ex. il. External iliac. 

 in.il. Internal ilia<'. 

 al. Allantoic vessels. 

 ep. Epigastric artery. 



