78 THE SENSORIAL FUNCTION. 



weight to support, but it is exposed to many injuries from tlie brutality of tliose by 

 whom he should be protected, and from accidental causes. 



The roof of the sicull is com])osed of two plates of bone : the outer one hard and 

 tough, and tlie different parts dove-tailed together, so as not to be easily fractured ; 

 ^he inner plate being elastic. 13y the union of these two substances of different con- 

 struction, the vibration is damped or destroyed, so far as safety requires. 



On raising any part of the skull of the horse, the dense and strong inembrane 

 which is at once the lining of the cranium and the covering of the brain — the dura 

 iiiattr — presents itself, it is united to the membranes below by numerous little cords 

 or prolongations of its substance, conveying blood and communicating strength to the 

 parts beneath. Between this membrane, common to the cranium and the brain, and the 

 proper investing tunic of that organ, is found tiiat delicate gossamers' web, appropri- 

 ately called the arachnoid — 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 sympa- 

 thising with any inflammatory action produced by injury of the skull. 



Beneath is the proper investing membrane of the brain — the jna maier — 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. 



We now arrive at the brain itself. The brain of the horse corresponds with the 

 cavity in which it is placed (w, p. 72). It is a flattened oval. It is divided into two 

 parts, one much larger than the other — the cerebrum or brain, and the cerebellum oi 

 little brain (n, p. 72). In the human being the cerebrum is above the cerebellum, in 

 the quadruped it is belov,- ; and yet in both they retain the same relative situation. 

 The cerebellum is nearer to the foramen through which the brain passes out of the 

 skull (n, p. 72), and the continuation of the cerebrum passes under the cerebellum 

 (p, p. 72), in order to arrive at this foramen. In the human head this foramen is at 

 the base of the skull ; but in the quadruped, in whom the head is placed Wanting, it 

 is necessarily elevated. 



He who for the first time examines the brain of the horse will be struck with its 

 comparative diminutive size. The human being is not, generally speaking, more 

 than one-half or one-tliird of the size and weight of the horse ; yet tlie brain of the 

 biped is twice as large and as heavy as that of the quadruped. If it had been the 

 brain of the ox that had been here exposed, instead of that of the horse, it would not 

 have been of half the bulk of that of the horse. If the dog had been the subject, it 

 would have been very considerably larger, comparing the general bulk of each animal. 

 This is singular. The human brain largest in comparative bulk ; then the brain of 

 the dog, the horse, the ox. Thus would they be classed hi the scale of intelligcnoe. 



If the brain is more closely examined, it will be found that there is none of the 

 roundness and the broadness of that in the human being ; it is comparatively tame 

 and flat. There is some irregularity of surface, some small projections and depres- 

 sions ; but they, too, are comparatively diminutive and inexpressive. Were the 

 brain of the beaver, of the hare, or the rabbit, or of almost any bird, substituted for it, 

 there would be no convolutions or irreg-ularities at all. 



These irregularities are not so Ijold and so deep in the ox as in the horse, nor in the 

 horse as in the dog. We do not know enough of the functions of any part of the 

 brain to associate these convolutions with any ])articular powers of mind, or good or 

 bad propensities, although some persons, who are wise above that which is written, 

 have pretended to do so. It would occupy too great a portion of this volume to ente. 

 into these questions; but there are some diseases to which the horse is subject, and a 

 very useful operation — the division of some of the nerves for certain purposes, and 

 which could not be understood without a previous slight account of this important 

 organ. 



When the brain is cut, it is foimd to be composed of two substances very unlike in 

 appearance (/«, p. 72) ; one, principally on the outside, grey, or ash-coloured, and 

 therefore called the cortical (I)ark-li/a) from its situation, and cineritious {ashen) from 

 its colour ; and the other, lying deeper in tlie brain, and from its pulpy nature calleu 

 the medullary substance. Although placed in apposition with each other, and seem- 



