292 



SYSTEMATIC ZOOLOGY. 



to do with the haemal arches. Hence it follows that the 

 ribs in a fish and those in a higher vertebrate a bird or 

 man, for example are not identical; i.e., are not homol- 

 ogous. The centra of the vertebrae may be hollow at either 

 end (amphiccelous) , as in fishes, or they may be hollow 

 behind and rounded in front (opisthoccelous) , as in the sala- 

 manders ; or again, they may be hollow in front and convex 

 behind (proccelous) , as in many reptiles; or lastly, they may 

 have flat surfaces, as in most mammals. 



The vertebral column is capable of division into regions. 



FIG. 102. Diagram of the skeleton of a mammal, showing regions of vertebral 

 column, etc. d, cervical; e, thoracic; /, lumbar; g, sacral; h, caudal verte- 

 bra; i, scapula; k, humerus; I, radius; m, carpus; n, ulna; o, metacarpus; 

 p, pelvis; r, femur; s, fibula; t, tibia; M, tarsus; v, metatarsus; w, phalanges; 

 y, sternum. 



In the fishes there are two of these, trunk and caudal, the 

 former being distinguished by bearing ribs. In the Am- 

 phibia a cervical region is distinguished from the trunk by 

 the absence of transverse processes from its single vertebra, 

 while the caudal is separated from the trunk by a sacral 



