CHORD. VI. \ 



357 



orally distinguish four regions, head, neck, trunk, and tail ( Fig. 

 352); but the neck may "be practically absent, as in whales and 

 their allies, and the tail may disappear as an external append.. 

 as in man. The head bears the mouth, which is provided with 

 movable lips in all groups except the lowest, which have a 



FlG. 352. Lepus cuniculus, the rabbit; lateral view of skeleton, with outline of body. 



(After Parker and Haswell.) 



horny beak like that of some birds. The external nares are 

 generally at the tip of the snout, and the olfactory organ is 

 more highly developed than in any other class of vertebrates. 

 The eyes are usually well developed and are provided with lids, 

 but are non-functional in some species which live habitually in 

 the dark ; connected with them are the lachrymal or tear glands. 

 External ears are usually well developed. 



As the Mammalia are of particular interest, being the most 

 highly developed group of animals and the one to which man 

 belongs, we may give an epitome of the more important internal 

 organs (Fig. 353). The axial skeleton consists of the skull and 

 vertebral column ; in the skull the sutures persist to a greater or 

 less extent throughout life. Five regions can be distinguished in 

 the vertebral column: the cervical region immediately succeeds 

 the skull, and the first and second vertebra' are known resp 

 tively as the atlas and the axis ; the skull rests on tin- atlas ; the 

 thoracic region succeeds the cervical, and each thoracic vertebra 

 bears a pair of ribs; most of the ribs join the sternum on the 

 ventral side of the bodv ; next comes the lumbar region, wh 

 the vertebras are without ribs; then the sacral region, 



