42 



MORPHOLOGY OF THE VERTEBRATE BODY 



teristic of the group as a whole. Endoskeletons and exoskeletons 

 alike serve as protective and supporting devices to which muscles 

 may be attached; but here the similarity ends (Fig. 22). In 

 the one case, the muscles are attached to the outer surface of the 

 skeleton; in the other, to the inner surface of a tubular covering. 

 Hence the mechanics of the two systems are ahke only insofar as 



Fig. 22. — Endoskeleton and exoskeleton in relation to soft parts of the body, 

 as shown by leg of man and of the grasshopper, 



(Redrawn from Pearse, " General Zoology," copyright, 1917, by Henry Holt and Co , 

 printed by permission.) 



the contraction of muscles causes movement in the parts to which 

 they are attached. In addition to muscles, the flesh contains 

 nerves and blood vessels and, in places, glands, the whole being 

 bound together by the so-called connective tissue. 



Mouth Cavity. — Passing to internal features, we see that the 

 mouth region of the frog (Fig. 23) offers some interesting contrasts 

 with the conditions occurring in man and the famihar mammals 

 (Fig. 24). The most obvious difference is that the nostrils of the 

 frog lead directly into the anterior end of the mouth, whereas in man 

 they lead into an extensive nasal chamber communicating with the 



