II. THE SKELETAL SYSTEM 



As the skeleton largely determines the general form of the 

 body and as locomotion and means of getting food are condi- 

 tioned by its structure, a study of the skeletal system should 

 reveal some interesting phases of comparative anatomy. 



For convenience the vertebrate skeleton may be divided as 

 follows : 



Axial skeleton 

 Skull 



Cranium (neurocranium) 

 Visceral skeleton (splanchnocranium) 

 Vertebral column 

 Ribs 

 Sternum 

 Appendicular skeleton 



Pectoral girdle and fore limbs 

 Pelvic girdle and hind limbs 



^iJlxial Skeleton 



VERTEBRAL COLUMN, STERNUM AND RIBS 



All members of the phylum Chordata at some time during 

 life possess a notochord. In most vertebrates this skeletal rod 

 is replaced in later life by a series of bones, the vertebrae, 

 closely articulated with one another, and forming the vertebral 

 column or backbone. The presence of this vertebral column 

 is one of the most distinguishing features of the vertebrates. 

 Within the chain of vertebrae lies the neural canal, containing 

 the spinal cord. 



Vertebral Column and Ribs of the Shark 



The division of the vertebral column into regions is largely, 

 though not wholly, dependent upon the presence of limbs. 

 In forms where limbs are lacking (e.g., snake), and in animals 

 that do not depend on the limbs for support, as in many aquatic 



