32 STRUCTURES OF THE BODY. 



ness of grain of the latter is clue to the thickness of the 

 layers of connective tissue which run through it. As 

 connective tissue has only the passive action of support, 

 it is evident that the coarser in grain a muscle is, 

 the less powerful will it be ; although it will be better 

 able to resist the effects of external violence than one of 

 finer grain. The protective duty of connective tissue, 

 as regards muscles, may be readily inferred from the fact 

 that the less exposed miiscles are to injury from with- 

 out, bv reason of their position, the less connective tissue 

 do they contain. This tissue, also, forms ligaments and 

 tendons, and ensheathes bones, cartilages, nerves, etc. 

 There is always a large amount of it immediately under- 

 neath the skin, in the form of loose fibrous sheets, as we 

 may see in the dead animal. The presence of a great 

 quantity of it in this position naturally causes the 

 underlying parts to be ill-defined, a fact which is 

 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. With age, the amount of connective 

 tissue in the body greatly increases. As Guerin 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." 



