554 APPENDIX. 



on the upper surface of the head is well adapted 

 for that purpose, being the first part that comes 

 to the surface of the water in the natural progres- 

 sive motion of the animal ; and therefore it is to 

 be considered principally as a respiratory organ, 

 and where it contains the organ of smell, that is 

 only secondary. 



The size of the brain differs much in different 

 genera of this tribe, and likewise in the propor- 

 tion it bears to the bulk of the animal. In the 

 Porpoise, I believe, it is largest, and in that re- 

 spect comes nearest to the human. The size of 

 the cerebellum, in proportion to that of the cere- 

 brum, is smaller in the human subject than in any 

 animal with which I am acquainted. In many 

 quadrupeds, as the Horse, Cow, &c. the dispro- 

 portion between the cerebellum and cerebrum is 

 not great, and in this tribe it is still less ; yet not 

 so small as in the bird, &c. The whole brain in 

 this tribe is compact, the anterior part of the cere- 

 brum not projecting so far forwards as in either 

 the quadruped or in the human subject; neither 

 is the medulla oblongata so prominent, but flat, 

 lying in a kind of hollow made by the two lobes 

 of the cerebellum. 



The brain is composed of cortical and medullary 

 substances, very distinctly marked ; the cortical 

 being, in colour, like the tubular substance of 

 a kidney ; the medullary very white. The sub- 

 stances are nearly in the same proportion as in 

 the human brain. The two lateral ventricles are 

 large, and in those that have olfactory nerves are 



