l.'l.] THE FROG. 85 



f$. The innominate vein; formed by the union of 

 the internal jugular vein, seen just behind the 

 angle of the jaw, and bringing back the blood 

 from the brain, spinal cord, and deep-seated 

 parts of the head, with the subscapular vein 

 returning the blood from the muscles of the' 

 shoulder. 



y. The axillary vein; formed by the union of the 

 subclavian vein which returns the blood from the 

 arm, with a large vessel (great cutaneous) bring- 

 ing back the blood from the integument. 



7. The pulmonary veins. 



These are exceedingly conspicuous in spite of 

 their small size, on account of the black densely 

 pigmented nature of their walls. On raising the 

 ventricle they are seen arising along the inner faces 

 of the lungs and uniting just before entering the left 

 side of the atrium (1. auricle) ; the right one is, of 

 necessity, the longer of the two. 



8. The system of the aortic arches. 



These may be dissected in the same animal; there 

 are three sets of vessels on each side, arising from 

 the truncus arteriosus. They may be readily distin- 

 guished from the great veins by their pinkish colour, 

 due to the presence of a small quantity of blood, and 

 by the thickness of their walls, the latter being very 

 obvious in the case of any one of the larger arteries 

 as whitish contour lines. 

 a. The anterior or carotid arch, concerned with the 

 blood supply to the head; it arises on each side 

 as a short trunk (common carotid') which early sub- 

 divides into — 



