250 ANATOMY, PHYSIOLOGY, &C. 



The Brain or Cerebrum. 



The brain weighs from two and a half to four 

 pounds, and has no fixed relation to the weight or 

 stature ; indeed, it varies very little in individuals. 



In man, the ratio of the weight of the brain to that 

 of the whole body, has been stated on an average at 

 about -g^th ; in the dog, -j^jth ; in the horse, ^J^th ; 

 and in the elephant, ^^th only ; while, on the con- 

 trary, in several of the small singing birds, and parti- 

 cularly in the canary, the brain is above the average 

 of man, being so much as -j\th. Among insects, the 

 humble-bee has the largest brain, in proportion to the 

 size of its body. In the radiata mollusca, the nervous 

 matter appears to be disseminated among the different 

 organs, and never appears in the form of a brain and 

 its connecting filaments. 



The Cerebellum, or Little Brain. 



This is the lower or little brain, which occupies 

 the lowest part of the encephalon, and weighs five or 

 six ounces. 



The developement of the cerebellum is simultane- 

 ous with that of the organs of generation at the age 

 of puberty. Early emasculation prevents its deve- 

 lopement, as well as of the beard, and organs of the 

 voice. 



Division of the Brain. 



There is a dense membrane projecting directly 

 downward to a considerable depth from the upper 

 part of the skull, and extending from the fore to the 

 back part of the head, which divides the brain into 

 two hemispheres ; the cerebellum is likewise divided 

 by a similar membrane into two hemispheres. 



The spinal chord or marrow has a longitudinal 

 furrow dividing it imperfectly into halves, analogous 

 to the hemispheres of the brain. 



