245 



LECTURE XIII. 



ON THE STRUCTURE OF THE SKULL. 



THE SKULLS OF MAMMALIA. 



We have met with no important difficulties in the way of 

 identifying the bones of the Bird's skull with those found in the 

 skulls of the Pieptilia and still lower Vertebrata ; and hence, 

 if the cranium of a Mammal be compared with that of a Bird, 

 the bones which correspond in the two will obviously be homo- 

 logous throughout the series. 



The accompanying figure represents a longitudinal and 



Fig. 97. 



SO 



Fio - . 97. — Longitudinal and vertical section of the cranial cavity of a Beaver. 



vertical section of the skull of a Beaver {Castor fiber), drawn of 

 the same absolute length as the section of the Ostrich's skull 



