14 



INTRODUCTION. 



pact whole. While, in the lower classes, the brain is, as it were, spread 

 out, and its component parts thrown asunder, it is here braced up, if the 

 expression may be allowed, to the establishment of a full communication 

 between its hemispheres and their dependencies ; and, consequently, to the 

 more perfect connexion of every part of the great nervous system concen- 

 trated in this focus. It may be observed, too, that the great sympathetic 

 nerve is here the most fully developed, and most thoroughly blended with 

 the spinal and cranial nerves. Constituting a system of its own, forming 

 ganglia along the spinal column, and in the cavities of the chest and abdo- 

 men, as well as plexuses, or intricate meshes, whence the vital organs are 

 abundantly supplied, it pervades the whole of the nutritive system, and 

 constitutes a chain of communication, a bond of mutual dependance, and 

 the source of harmony of action between all the organs of animal and 

 vegetative life, the functions of which depend upon its agency. 



Much has been said by anatomists and physiologists respecting the 

 weight of the brain compared with that of the body, but with very inconclu- 

 sive results : it has, moreover, from very early times, been asserted, that 

 Man has not only a brain comparatively larger, with regard to the weight 

 of the body, than the lower animals, but that he has positively a larger 

 brain than any of them ; neither of these propositions is absolutely true. It 

 is in the development of the cerebral hemispheres, the complexity and 

 volume of the apparatus (especially of the corpus callosum), by which 

 its several parts are brought into communication, and the increased ex- 

 tent given to the surface of the hemispheres, by means of the convolu- 

 tions, that the brain of Man rises above that of other Mammalia. 

 Nevertheless, the size of the human brain is a remarkable character ; 

 but, as if to prove that its superiority consists in the arrangement and 

 development of its parts, it is smaller, compared with the bulk of the 

 body, than in many of the passerine birds ; and though it absolutely 

 exceeds the brain of some of the large Mammalia, it does not exceed the 

 brain of all. In the Rhinoceros, however, it is smaller than in Man ; for 

 Sparrman found the cranial cavity, in the enormous two-horned Rhino- 

 ceros of Southern Africa, to'be only six inches long and four inches deep ; 

 and, on filling a skull of this animal with peas, it barely contained one 

 quart ; while a human skull, measured at the same time, required nearly 

 three pints to fill it. Tiedemann observes, that the brain, in the average 

 of the human race, attains its full size towards the seventh or eighth 

 year.* Its weight in the male f varies, between three pounds three ounces, 



* Soemmerring says, erroneously, that the brain does not increase after the third year. Gall and 

 Spurzheim, on the other hand, are of opinion, that it continues to grow till the fourteenth year. The 

 brothers Wenzel have shewn, that the brain arrives at its full growth about the seventh year ; and 

 this is confirmed by Hamilton's researches. 



t The brain of Cuvier weighed four pounds eleven ounces four drachms and thirty grains, Troy 

 weight ; that of the celebrated surgeon, Dupuytren, four pounds ten ounces, Troy. 



