502 



ANATOMY OF VERTEBRATES. 



Capillaries with blood-discs of the web of the foot, 

 Frog, magu. cclxvii. 



331 



the eye the circulatory motion of the blood, flowing constantly 



from the arteries to the veins, as seen, e.g. by transmitted light 



330 in a membranous part of 



the frog's or newt's struc- 

 ture, under the micro- 

 scope, fig. 330. 



The venous system of 

 Batrachians resembles that 

 of Fishes in the degree in 

 which the species retain 

 the piscine character. The 

 cardinal veins, essentially 

 those which return the 

 blood from the osseous and 

 muscular segments of the 

 trunk, are largest in the 

 Perennibranchs, and de- 

 crease, as the hind-limbs 

 acquire more size and 

 power, in the Newts and 

 Land -Salamanders, until, 

 in the tail-less and long- 

 leowd Frogs and Toads, 

 the primitive venous trunk 

 of the body is reduced 

 to the condition of the 

 f azygos' vein in Mammals, 

 and the great bulk of the 

 blood is submitted to the 

 influence of the kidneys 

 and liver before it is re- 

 turned to the heart. 



In the Frog, fig. 331, the 

 blood being collected from 

 each hind-limb into an is- 

 chiadic and iliac vein, these 

 unite into a common iliac 

 vein, which divides. One 

 branch joins that of the 

 opposite iliac, and receiyes 

 the vein of the great allan- 



Cire.ulat ion in the Frog, cclxvii. , , , , /. ,i 



toic bladder, to form the 

 < umbilical vein,' fig. 331, u : the other branch, K, goes to the 



