INTRODUCTION. 83 



metatarsus, and toes. The extremities are greatly 

 liable to vary in different orders and genera ; in some, 

 those of the fore parts being lengthened, so as to 

 form the supporters of a wing, as in bats ; in others, 

 shortened, as in jerboa and kangaroo ; while, in both 

 the last mentioned, the posterior extremities are en- 

 larged to an apparent disproportion. Cetacea and 

 analogous animals have not only no pelvis, but their 

 hinder extremities are likewise wanting, having in 

 their stead, at the end of the vertebral column or 

 spine, cartilaginous bodies, forming a kind of feet, or 

 the flukes of the tail, which, with them, is always 

 horizontal. 



The head of mammalia is, in all cases, articulated 

 by two condyles upon their atlas or first vertebra : 

 As the seat of intelligence, it has excited the greatest 

 interest in all ages ; and it has been remarked, that 

 the approach to reason, observed in animals, bore 

 some relation to the size and configuration of the 

 head. As the brain is the centre, or origin of the 

 nervous system, it may be proper to enter into a 

 general anatomical detail of its structure. The brain 

 proper, or cerebrum, consists of two large lateral 

 lobes or hemispheres, and of the anterior and middle 

 lobes. It is divided by a strong membrane from 

 the cerebellum, or smaller brain, which occupies the 

 lower and posterior part of the cranium. The sur- 

 face of the brain presents a convoluted appearance, 

 and is of a pale reddish-grey colour ; but this is only 

 superficial; and if a portion be removed, the in- 

 terior is white : the lateral hemispheres are deeply 



