6b THE BRAIN 



eating otreligth to the parts beneath. Between this membrane 

 common to the cranium and the brain, and the proper investing 

 tunic of that organ, is found that delicate gossamer's web, appro- 

 priately called the arach/rurid — ^the spider's membrane — and 

 which is seen in other animals, designed either to secrete the 

 fluid which is interposed, for the purpose of obviating injurious 

 concussion, or perhaps, to prevent the brain from readily sym- 

 pathizing with any inflammatory action produced by injury of 

 the skull. 



Beneath is the proper investing membrane of the brain — ^the 

 fna mater — which not only covers the external surface of the 

 brain, but penetrates into every depression, lines every ventricle, 

 and clothes every irregularity and part and portion of the brain. 



The Brain. — ^We now arrive at the brain itself. The brain 

 of the horse corresponds with the cavity in which it is placed 

 {m, Fig. 3). It is a flattened oval. It is divided into two parts, 

 one much larger than the others — ^the cerehrv/m or brain, and 

 the cerebellum or little brain (»i. Fig. 3). The brain of a horse 

 is only about half the size and weight of that of a man. 



When the brain is cut, it is found to be composed of two sub- 

 stances very unlike in appearance (m. Fig. 3) ; one, principally on 

 the outside, gray, or ash-colored, and therefore called the cortical 

 {bark-like) from its situation, and cineritious (ashen) from its 

 color ; and the other, lying deeper in the brain, and from its 

 pulpy nature called the medullary substance. Although placed 

 in apposition with each other, and seemingly mingling, they 

 never run mto the same mass, or change by degrees into one 

 another, but are essentially distinct in construction as well as in 

 function. 



The medullary portion is connected with the nervous system. 

 The nerves are prolongations of it, and are concerned in the dis- 

 charge of all the offices of life. They give motion and energy 

 to the limbs, the heart, the lungs, the stomach, and every part 

 connected with life. They are the medium through which sen- 

 sation is conveyed ; and they supply the mind with materials to 

 think and work upon. 



The cineritious part has a different appearance, and is differ- 

 ently constituted. Some have supposed, and with much appear- 

 ance of truth, that it is the residence of the mind — ^receiving the 

 impressions that are conveyed to the brain by the sensitive 

 nerves, and directing the operation and action of those which 

 give motion to the limbs. 



From the medullary substance — as already stated — ^proceed 

 certain cords or prolongations, termed nerves, by which the ani- 

 mal is enabled to receive impressions from surrounding objects, 

 and to connect himself with them ; and also to possess many 



