STRUCTURAL AND SYSTEMATIC ZOOLOGY 



ventral, or hemal, cavity cor- 

 responds to the whole body 

 of an invertebrate; while 

 the dorsal, or neural, is 

 mainly additional. 



Vertebrates are also dis- 

 tinguished by an internal, 

 jointed skeleton, endowed 

 with vitality, and capable of 

 growth and repair. During 

 embryo life it is represented 

 by the notochord ; but in the 

 higher forms this is after- 

 ward replaced by a more 

 highly developed vertebral 

 column of cartilage or bone. 

 The column and cranium 

 are never absent in the Cra- 

 niata; other parts may be 

 wanting, as the ribs in frogs, 

 limbs in snakes, etc. The 

 limbs are never more than 

 four, and are always articu- 

 lated to the hemal side of the 

 body, while the legs of inver- 

 tebrates are developed from 

 the neural side. The mus- 

 cles moving the limbs are at- 

 tached to the endo-skeleton. 



The circulation of the 

 blood is complete, the arte- 

 ries being joined to the veins 



FIG. 112. Diagram of circulation in the , .,, , , 



higher vertebrates: i, heart; 2, lungs; by CaplllariCS, SO that the 



J\TS^Ti i S blood never esca P es into 



tremities; 8, liver. (From Dalton's the visceral Cavity as in the 

 " Physiology.") 



