VERTEBRAT A . 



307 



by a more highly developed 

 vertebral column of cartilage 

 or bone. The column and 

 cranium are never absent in 

 the craniota ; other parts may 

 be wanting, as the ribs in Frogs, 

 limbs in Snakes, etc. 154 The 

 limbs are never more than 

 four, and are always articu- 

 lated to the hsemal side of the 

 body, while the legs of Inver- 

 tebrates are developed from 

 the neural side. The muscles 

 moving the limbs are attached 

 to the endoskeleton. 



The circulation of the blood 

 is complete, the arteries being 

 joined to the veins by capil- 

 laries, so that the blood never 

 escapes into the visceral cav- 

 ity as in the Invertebrates. 

 All have a portal vein, carry- 

 ing blood through the liver; 

 all have lacteals and lym- 

 phatics. The blood is red, 

 and contains both kinds of 

 corpuscles. 155 The teeth are 

 developed from the dermis, 

 never from the cuticle, as in 

 Mollusks and Articulates ; the 

 jaws move vertically, and are 

 never modified limbs. The 

 liver and kidneys are always 

 present. The respiratory or- 

 gans are either gills or lungs, 



Fig. 281. —Diagram of Circulation in 

 the higher Vertebrates : 1, heart ; 2, 

 lungs ; 3, head and upper extremities ; 

 4, spleen; 5, intestine ; 6, kidney; 7, 

 lower extremities ; 8, liver. ( From 

 Dalton's "Physiology.") 



