Book VII. PHYSIOLOGY OF THE HORSE. 899 



thoracic duct, which, passing up by the side of the aorta, pours its contents into the heart through the 

 medium of the jugular vein. The lymphatic absorbents differ from the latter only, in being situated over 

 the whole body, and being the recipients of the various matters of the body ; whereas the lacteals appear to 

 absorb the eliyle only. From numerous facts, we know that the various organs are continually suffering 

 a destruction and a removal of parts, and that what the absorbents take away, the arteries renew ; and 

 to this constant change, most of the alterations of the body are to be attributed as regards the structure 

 of parts. We use our power over these vessels in the horse medicinally. We stimulate the absorbents 

 to take up diseased solutions of fluids from various parts of the body, as in watery swellings in the legs by 

 mercury, and by friction, or by pressure in the way of bandage. When deposits are made of hard matter, 

 on ligament or bone, we stimulate them by blistering or by firing. It is by stimulating the absorbents 

 that splints and spavins are removed. Exercise is a very powerful stimulus to absorbents ; thus it is 

 that swelled legs are removed by half an hour's exercise. In the horse, the lymphatics are more liable 

 to disease than the lacteals, but in man the reverse. Farcy diseases the lymphatics irreparably. 



SuBSECT. 4. Nerves and Glands of the Horse. 



."5681. The nervous system of the horse is composed of white medullary cords, springing from the brain 

 and spinal marrow, "whence they are generally distinguished into the cerebral and spinal nerves : the 

 internal structure of these bodies is fibrous, and their ramifications extend to every part of the body; it 

 is supposed that the brain is the seat of sensation and volition, and that the nerves are only the messengers 

 of it. The sensibility of a part is usually proportioned to the number and size of its nerves ; nervous in- 

 fluence occasions motion. From some cause, unknown to us, some motions are voluntary, and some 

 involuntary ; but both are brought about by nervous agency. As the nerves are the media of sensation ; 

 so a division of their cords has lately been attempted, with success, to relieve certain painful affections ; 

 the most prominent instance is, in the division of the pastern nerves for the relief of the painful 

 affection of founder. Tetanus, or locked jaw, which seems a morbid irritation on the nerves, has been 

 recommended to be treated in the same way. 



5682. The cerebrine nerves, arising in pairs immediately from the brain, are the olfactory, optic, motores 

 oculi, pathetici, trigemini, abducents, auditory, lingual, par vagum, and the pair called the intercostal or 

 g7-eat sympathetic, from its extensive connection. 



5683. The spinal nerves are those which arise immediately from the spinal marrow, as the cervicals, hu~ 

 merals, ulnar, metacarpal, and pastern nerves^ the dorsal, the lumbar, crural, sciatic, popliteal, sacral, 

 and the nerves^ to the posterior extremities, which correspond with those of the anterior. 



5684. The glands are numerous, and placed in every part of the body; they may be characterized as 

 secretory bodies, composed of all the different vessels inclosed in a membrane ; their oflSce appears to be 

 to secrete or form some fluid, as the liver secretes bile, and the kidney urine. They are classed into 

 folliculose, globate, glomerate, and conglomerate; they also receive specific. names according to their 

 situations, or according to the fluid they secrete, as lachrymal, salivary, &c. 



SuBSECT. 5. Integuments of the Horse's Body. 



5685. The common integuments may be considered as the hair, the cuticle, the epidermis, or in- 

 sensible or outer skin, the rete mucosum, which is immediately under this, the cutis, sensible or true skin, 

 the cellular membranes, which contain fat and other fluids, and the panniculus carnosus or fleshy pan- 

 Hide ; to these rnay be added, the unguis, nails or hoofs, which we shall describe separately. 



5688. Hair is the clothing of brutes, and hence is very important to them, and as it enters largely into 

 the arts, it is also important to us. (1814.) It appears to be a production of the true skin, arising from a 

 bulbous end, which penetrates the rete and cuticle in the form of an elongated cone. In some parts hairs 

 appear, singly, as about the muzzle ; in others in masses, as on the mane, tail, and over the body generally, 

 as an inclined congregated mass ; hair varies in color, and therefore appears by nature intended both for 

 ornament and use. 



5687. The cuticle is situated immediately under the hair (1807.), and appears a hard insensible cover- 

 ing, purposely placed to guard or defend the sensible skin underneath. The cuticle lines many of the large 

 openings of the body, as the mouth, from whence it is continued into the stomach, lining one half of it. It 

 is perforated by innumerable small vessels that give' out and take in various matters; through these 

 blisters act on the true skin, inflame it, and force it to secrete a quantity of fluid, which thus pushes the cuticle 

 from the cutis. It exists before birth, and is speedily renewed afterbirth, when accidentally destroyed, and, 

 like the true skin, thickens by pressure ; it is constantly undergoing changes ; it exfoliates in the form of 

 powder, or little scales, over every part of the body, and is that substance called dandriff, which grooms are 

 80 careful to remove with the currycomb. The rete mucosum is a mucilaginous substance placed hke a 

 net between layers of cuticle and cutis ; and although very universal in animated nature, its ^use is 

 unknown, 



5688. The cutis, corium, or true skin. (1810) This very general investure of the body is situated imme- 

 diately under the two former ; it is very vascular, and is furnished with innumerable small villous processes o f 

 exquisite sensibility, and which, without doubt, were intended to constitute it as the real organ of touch. 

 It is much thickened by pressure ; asses, from the beatings they are subjected to, have it of immense thick- 

 ness on the rump. It naturally also exists in various degrees of density according to the wants of the 

 animal. Like the cuticle it is perforated by numerous openings which correspond with those of the latter 

 membrane. Its composition appears principally gelatine, and hence it is employed in the manufacture of 

 glue ; its gelatine uniting with the matter called tannin, becomes insoluble in water, and then forms 

 leather ; and the value of the horse's hide in this particular is sufficiently known. 



5689. Adipose membrane and fat. These form very considerable parts of the body of most animals. 

 The adipose membrane is not so universal as the skin ; some parts are completely without it, as the eyelids, 

 ears, sheath, and some parts of the extremities. It is cellular, but the cells fortunately do not communicate 

 or the fat would gravitate. The/a/ is the unctuous juice poured or rather secreted into these cells. Itap-^ 



Eears in greater quantities, and in different degrees of consistence in some parts than in others: in the 

 elly of some it is lard, and suet in others; within the bones it is oleaginous in all. DiflFerent quadrupeds 

 have their fat of different degrees of consistence, from the firm suet of the ox, and the tallow of the sheep, 

 to the soft lard of the hog, and the intermediate state of the horse ; it guards the parts, it preserves warmth, 

 but above all, it is a depot against occasional want : thus a fat animal can sustain itself without food much 

 longer than a lean one. The torpid bear comes from his hibernation emaciated, because his constitution 

 has been subsisting on his fat. 



5690. Cellular membrane. (1812.) This complete investure of the body enters every part, and is 

 formed of communicating cells, as we see by the practice of butchers who blow up their meat'; and also by 

 the emphysematous effects of a fractured rib, and the gaseous distention in some putrid diseases ; it exists 

 in different quantities, and under various modifications of density throughout the body, and is a very uni-^ 

 versal medium of connection in the form of ligament. 



5691. Pannicuhts carnosus. (1819.) The fleshy pannicle was kindly given to quadrupeds in lieu of hands, 

 to enable them to corrugate or pucker the skin, and thus to shake off dust and insects. It is a thin 

 muscular expansion peculiar to brutes, but not to all ; the swine family being denied it. By its attach- 

 ments it can operate variously,, as we see by the uses the horse makes of it j it is very vascular, and 

 sensible also from the numerous nerves which enter it. 



3 M 2 



