350 Morton's Crania Americana. 



great power of smell, to 120 square inches. The optic nerve in 

 the mole is a slender thread, and its vision is feeble ; the same nerve 

 is large and thick in the eagle, accompanied by intense pov/ers of 

 sight. Again, the fact admits of demonstration, that deiiciency 

 in the size of the brain is one, although not the only, cause of 

 idiotcy. Although the brain be healthy, if the horizontal circum- 

 ference of the head, with the muscular integuments, do not ex- 

 ceed thirteen or fourteen inches, idiotcy is the invariable conse- 

 quence. Dr. Voisin states that he made observations on the 

 idiots under his care at the Parisian Hospital of Incurables, and 

 found that in the lowest class of idiots, where the intellectual 

 manifestations were null, the horizontal circumference, taken a 

 little higher than the orbit, varied from eleven to thirteen inches, 

 while the distance from the root of the nose backwards, over the 

 top of the head, to the occipital spine, was only between eight 

 and nine inches ; and he found no exception to this fact. If, 

 therefore, extreme defect of size in the brain be invariably accom- 

 panied by mental imbecility, it is a legitimate inference that size 

 will influence the power of manifestation through all other gra- 

 dations of magnitude, always assuming other conditions to be 

 equal. 



Physiological authorities are equally explicit on this subject. 

 Magendie says, '' the volume of the brain is generally in direct 

 proportion to the capacity of the mind. We ought not to suppose, 

 however, that every man having a large head is necessarily a per- 

 son of superior intelligence ; for there are many causes of an aug- 

 mentation of the volume of the head besides the size of the brain ; 

 but it is rarely found that a man distinguished by his mental fac- 

 ulties has not a large head. The only way of estimating the vol- 

 ume of the brain, in a living person, is to measure the dimensions 

 of the skull ,• every other means, even that proposed by Camper, 

 is uncertain." 



The difference of mental power between young and adult 

 minds, is a matter of common observation. The diflerence in 

 the weights of their brains is equally decided. 



According to Cruveilhier, in three young subjects, the weights 

 of the brains were as follows : 



In the first, the brain weighed 2 lbs. 2 oz. ; the cerebellum, 

 4^ oz. ; together, 2 lbs. 6^ oz. In the second, the brain weighed 

 2 lbs. 8 oz. ; the cerebellum, 3^ oz. ; together, 2 lbs. 11^ oz. In 



