THE BEAIN AND NERVES. 43 



an Incredible degree ; and thus in horses that liave been lame for 

 a long time in their feet, we find the muscles of the chest greatly- 

 diminished, from want of the same degree of exercise. From this 

 circumstance, farriers, mistaking the cause for the efiect, have 

 given the name of chest-founder to the disease. — Ed. 



CHAP. IX. 



ON THE BEAIN AND NEEVES. 



The brain, the seat of the mind, and the fountain of sensation, 

 is a soft body, situated in a cavity of the skull called the cranium. 

 In man it occupies by far the greater portion of the skull ; but, 

 in the horse, from its much smaller size, and from the large space 

 devoted to the face, the cranium is much the smaller part. It 

 usually weighs about one pound and a few ounces in the horse. 

 It is closely invested by a membrane, called the pia matey-, whilst 

 the cranium is lined by a firm, strong membrane, called the dura 

 mater. Between these there is another delicate membrane, called 

 the tunica arachnoides. 



The dura mater, by its duplications, forms several processes and 

 sinuses, the former, by descending between its divisions, serve to 

 secure the brain in its position, and the latter act as reservoirs 

 for the venous blood, thus preventing the brain from being 

 injured by any temporary imj)ediment to its passage. 



The pia mater closely embraces the brain, and dips into Its 

 convolutions. The brain consists of three parts, the Cerebrum, 

 the Cerebellum, and the Medulla oblongata. 



The Cerebrum is considerably the largest, and is divided into 

 two hemispheres, each of which closely corresponds with its 

 fellow. 



On cutting into the cerebrum, we find that it consists of two 

 portions, — the medullary, or white ; and the grey, or cortical 

 part. The latter is mostly situated towards the surface, and the 

 former towards the centre ; but both appear to run into each 

 other. Within the hemispheres there appear to be various 

 cavities, canals, and membranes, which, in this work, it is un- 

 necessary to describe. 



The Cerebellum, or little brain, is situated behind the cerebrum, 

 than which it is considerably smaller. It appears to consist of 

 medullary and cortical substance mingled together. 



The Medulla oblongata, the smallest division, is situated at the 

 base of the brain. It is medullary in its structure, and gives 

 origin to the greater part of the cranial nerves. It is by far the 

 most sensible part of the brain, for whilst portions of the cerebrum 

 have been cut away, in some animals, without giving any apparent 



