438 



ZOOLOGY 



run about, is it expelled from the oviduct (born) to live its 

 separate existence. 



Muscular System. — The muscles of mammals are developed 

 in close relation with the skeleton. On the head, besides a thin 

 sheet of skin muscles, the larg'e.st development is that of the 

 jaws. On the trunk is a general skin musculature and a pow- 

 erful dorsal musculature usetl in jumiiing. Then there is a 

 rudimentarv set of muscles uniting the ril>s, and a muscular 



T-i.h. 



Flu. 396. — Brain of the r:ilil)it si-cn from llif right side: h,,i, olfartnry 

 lobe; /./j, cereijruni ; JiJ'. rvi-:Av.-\\\\\\\ and it.s median leilie. c^'' : /i"l, 

 medulla oljlongata ; /)./■. the "ijeins" or Ijrii.lge of tran,s^-erse filjres ; hxti, 

 eranial ner\'es. After AA'iedersheini. 



membrane (or diaphragm) completely dividing the body cavity 

 into an anterior and a posterior portion. Both the ril) muscles 

 and chaphragm are used in breathing. Tlie musculature of 

 the appendages is the most jiowerfiil, Init so complex as to 

 be beyond the limits of such a book as this. 



Nervous System. — The central nervous system consists, 

 as in the iiigeon, (.)f a liruiu and spinal c<trtl. The chief advance 

 in the lirain is shown by the enlarged cerebrum, showing traces 

 of the foldings of its surface which l)ccome more marked in the 

 higher mammals and are a.ssociated with intelligence. 



