82 THE FROG CHAP, vi 



(rn) to the kidneys, and spermatic arteries (spni) 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 (it) which go to the hind-limbs. 



The pulmo-cutaneous trunk divides into two main 

 branches, the pulmonary artery (put) 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 ramifications 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 \he 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 confluence of several 

 veins, of which the most important are the external jugu- 

 lar (ext. ju) from the lower jaw and tongue, the internal jugu- 

 lar (int. ju] from the brain, eye, etc., and the subclavian (scl), 

 formed by the union of the brachial, from the fore-limb, and 

 the musculo-cutaneous (mu. cu\ already noticed, from the 

 superficial parts of the head and part of the skin and 

 muscles of the abdomen. 



With the posterior end of the sinus venosus is connected 

 a single large vein, the postcaval or vena cava posterior 



