430 THE ANATOMY OF THE HORSE 



To THE NAKF.D EYE an ordinary musolo appears to be composed of a 

 number of small bundles of fibres, arranged in parallel linca, and connected 

 by a fine membrane. These bundles may still further be separated into 

 what seems at first to be elementary fibres ; but wlien placed in the micro- 

 scope, they are found to be themselves made up of finer fibres united into 

 fasciculi by delicate filaments. These ultimate fibrilhe arc polyhedral in 

 section, according to the observations of INIr. Bowman, so as to pack closely 

 tOgethei-, and are variable in size in different classes and genera of animals. 

 They also differ in appearance, one class presenting stripes wliile the other is 

 without thom. The former includes all the muscles wliose movements are 

 under the control of the will as well as those of the heart, and .some of the 

 fibres of the a-.sophagus, while the latter is composed of the muscles investing 

 the stomach, intestines, bladder, etc., which aro comprehended under tho 

 general term involuntary. 



The Sarcolemma is the name given by 'Mv. Bowman to the areolar tissue 

 investing each fibre, sometimes also called myolemma. It is very delicate 

 and transparent, but tough and elastic ; in general it has no appearance of 

 any specilic structure, but sometimes it presents an aspect as if there was an 

 interweaving of filaments. 



When a fibkilla of striated muscle is examined under tiie microscope 

 of a high magnifying power, it is seen to present a beaded appearance, as 

 if made up of a linear aggregation of distinct cells, alternately light and 

 dark. When the fibrilla is relaxed, each cell is longer than it is broad ; 

 but, during the action of the muscle, it assumes the opposite dimensions, 

 the increase in one diameter being always in proportion to the diminution 

 of the other. As the contraction takes place the substance becomes firmer 

 than before, but the bulk remains the same, the mass merely gaining in 

 thickness what it has lost in length. The application of certain stimu- 

 lating agents will produce the contraction for a certain period after life 

 is destroyed, varying according to the vitality of the animal experimented 

 upon and the nature of the individual muscle. This is called irritability 

 in the striated muscles, which exhibit powerful contractions, alternating 

 with relaxations — while in the involuntar}" muscles a more steady, per- 

 manent, and moderate contraction is met with, to which the name of tonicity 

 has been given. 



Pi' re muscular fibre appears to be identical in composition with the 

 fil)rine of the blood, being made up of about seventy-seven parts water, 

 fifteen and a half parts fibrine, and seven and a half parts of fixed salts. The 

 whole of the flesh of the body is largely supplied with blood, and it is found 

 by experiment, on the one hand, that if this is cut off contraction ceases 

 very speedily after ; and on the other, that in proportion to the amount of 

 muscular action will be the demand for fresh supplies of blood. None of the 

 striated muscles, except the heart and the muscles of respiration, can go on 

 acting without intervals of rest, during which repairs in their structure are 

 effected. If, therefore, the voluntary muscles are to be brought into tho 

 highest state of vigour and development of size, they must be regularly 

 exercised and rested at proper intervals. During the former condition 

 blood is attracted to them, and at the same time that fluid itself is rendered 

 more fit for the p\irposes of nutrition ; while during the latter period the 

 increased flow of blood continuing allows for a complete reparation of the 



