THE NERVOUS SYSTEM. 13 



defined, a fact which will be especially noticeable about the 

 tendons and ligaments below the knees and hocks^ owing to 

 the absence of muscle about these parts. We may, therefore, 

 draw the following deductions : ( i ) That, as the thickness of 

 the skin is a measure of the amount of connective tissue it 

 contains ; the thicker the hide, other things being equal, the 

 more connective tissue will there be in and about the muscles. 

 (2) That, as its action is only passive, the more of it a 

 muscle contains, the slower will be the movements of the 

 muscle. Hence, we may reasonably conclude that the fact 

 of a horse having a thick skin, and, for instance, ill-defined 

 suspensory ligaments, owing to natural ''fleshiness,'' would 

 warrant us in supposing that he was deficient in speed, I 

 may remark that, with age, the amount of connective tissue 

 in the body greatly increases. As Gu^rin states : '^ In the 

 old man, the tendon seems to invade the muscle, so that 

 the portion of the calf of the leg which remains is placed 

 very high, and is much reduced in length. The muscles of 

 the loins and back present the same character. In old age 

 they are poorer in red fibre, but richer in tendon." 



The component parts of the body which, respectively, 

 have the same structure, are called iissues. Thus we have 

 bony tissue, consisting of bone ; muscular tissue, of muscle ; 

 nervous tissue, of nerve substance ; connective tissue, of 

 white fibrous material ; and so on. 



The Nervous System. — While considering the form of 

 the horse from a mechanical point of view, we must not lose 

 sight of the marked differences which exist in the nervous 

 system of various animals, and which greatly heighten, or 

 may altogether nullify, advantages obtained from good con- 

 formation. We are aware, speaking within reasonable limits, 

 that the amount of contraction — i.e. force — exhibited by a 

 muscle is proportional to the degree of stimulation given by 

 its nerves. As the nervous system of some animals acts far 

 more energetically than that of others, it follows that the 

 former, other things being equal, will be stronger than the 



