34 THE REASON WHY : 



" Far as creation's ample range extends, 

 The scale of sensual, mental powers ascends." POPE. 



90. The functions of the great and small brain appear to be regulated by a system 

 of mutual dependence and co-operation. During wakefulness the great brain, aided 

 by the influence of the small brain, and also by that of the spinal cord, conducts 

 and regulates the conscious movements of the body. But during sleep, when the 

 great brain relaxes the reins of government, and pives them over to the small 

 brain, this organ, being left to its own laws, directs, through its own fibres and 

 those of the spinal cord, the movements of the heart, lungs, and other internal 

 organs, acting at the same time on the muscles ; and while the small brain flows 

 into all these, there results a plenary equilibrium of the body, and a general 

 co-operation of all its parts for the mutual support of each other, and for the 

 preservation of the whole. 



91. IVhy is it that although the brain and the spinal cord are 

 so intimately connected, yet the brain is not affected by the violent 

 movements which the spine is constantly making ? 



The evil is partly obviated by the elastic and partly by the non- 

 elastic properties of the matter interposed between the several 

 layers of compact bone. By means of the elastic property of this 

 matter, the head rides upon the summit of the column as upon a 

 pliant spring, while the canal of the spinal cord remains secure and 

 uninvaded. By means of the soft and pulpy portion of this matter, 

 the vibrations excited in the compact bone are absorbed point by 

 point as they are produced ; as many layers of this soft and pulpy 

 substance, so many points of absorption of the tremors excited in 

 the compact bone, so many barriers against the possibility of the 

 transmission of a shock to the delicate nervous substance. 



92. Why may the form of the skull be sometimes changed 

 without injuring the brain ? 



Because the peculiar softness of the cerebral mass enables it to 

 undergo those changes of its envelope without inconvenience 

 The brain, in proportion to its softness, will suffer percussions am 

 pressures with less danger ; and, on this account, new-born children 

 whose bones are soft and moveable, may have their head? 

 compressed, and even deformed, without any bad effect. 



93. Among some of the savage tribes a low brow is regarded as a beauty f^d *> 

 secure this, the heads of infants are subjected to pressure from plates fixed oil the 

 top of the head, by which means, the crown of the head becomes periectty ua., 

 while the back portion of it protrudes extensively. 



