82 THE FROG CHAP, vi 



traceable to the liver (hp), stomach (gs), duodenum 

 (du), spleen (spl), and ileum (int], 



The dorsal aorta gfives off on either side four renal 

 arteries (rn) to the kidneys, and spermatic arteries (spm) 

 in the male, or ovarian in the female, to the reproductive 

 organs, and at the posterior end of the abdominal 

 cavity divides into the right and left iliac arteries (il), 

 which go to the hind-limbs. 



The pulmo-cutaneous trunk divides into two main 

 branches, the pulmonary artery (pul) which goes to the 

 lung, and the cutaneous artery (cu\ which forms an 

 extensive system of branches over the skin. 



With proper care all these arteries can be traced into 

 the various organs to which they are distributed, when 

 they will be found to branch repeatedly, sending rami- 

 fications to all parts. The iliac artery, for instance, 

 may be followed along the whole length of the leg, 

 giving off branches to all the muscles, to the skin, and 

 to the digits, with their intervening web. 



The Veins. Since every part of the body has its vein 

 as well as its artery, there is a rough correspondence 

 between the two kinds of blood-vessel. The arrange- 

 ment of the principal trunks is, however, very different 

 in the two cases. 



On either side of the base of the heart is a large vein 

 called the precaval or vena cava anterior (Figs. 3 and 21, 

 pr. cv) : by turning the ventricle aside, the two precaval 

 veins can be seen to join the anterior end of the sinus 

 venosus (s. v). Each precaval is formed by the con- 

 fluence of several veins, of which the most important 

 are the external jugular (ext. ju) from the lower jaw and 

 tongue, the internal jugular (int. ju} from the brain, eye, 

 etc., and the subclavian (scl), formed by the union of the 

 brachial(br) ,from the fore-limb, and the musculo-cutaneous 

 (ms. cu), already noticed, from the superficial parts of 



