2 ELEMENTARY BIOLOGY. [CHAP. 



a. Its general arrangement. 



1. The central axis, consisting of the vertebral or spinal 

 column and of the central parts of the skull which 

 lie, in front of the spinal column, in the same antero- 

 posterior line. 



2. Lateral parts, supported, directly or indirectly, by 

 the axis. 



a. The appendages proper. (Limits and limb-arches.} 

 a . The fore-limbs : their supporting shoulder-girdle 



or pectoral arch, not directly attached to the 

 axial column; the limb proper; its main di- 

 visions; humerus, radius and ulna (the two 

 latter ankylosed), carpus and digits. 

 /?. The hind-limbs : their supporting arch (pelvic 

 girdle), carried directly by bony processes 

 proceeding from the vertebral column; the 

 limb proper ; its main divisions, os femoris, 

 tibia and fibula (ankylosed), tarsus, digits. 



b. The facial and lateral cranial bones. 



b. The vertebral column. 



It consists of an anterior segmented portion (each 

 segment being a vertebra) and of a posterior un- 

 segmented portion (the urostyle). 



i. Examine carefully and draw various aspects of a de- 

 tached vertebra, say the third. 



a. Its solid flattened ventral part centrum)', with 

 an anterior concave and a posterior convex 

 surface. 



b. The neural arch: an arch of bone springing 

 from the sides of the dorsal aspect of the cen- 



