370 MUSCULAR MOTION. 



the pellucid substance inclosed it >on all sides; appearances which 

 have been considered to show, that the elementary particles of which 

 the fibril is composed are little masses of pellucid substance, possibly 

 nucleated cells, presenting a rectangular outline, and appearing dark 

 in the centre. 



The ultimate fibres or filaments, when united in bundles, form fas- 

 ciculi or lacerti; and these, by their aggregation, constitute the various 

 muscles. Each fibre, each lacertus, and each muscle, is surrounded by 

 a sheath of areolar tissue, which enables them to move readily upon 

 each other, and preserves them in situ. The fibres are not the same 

 at the extremities as they are at the middle. The latter only consist 

 of the proper muscular tissue; the extremities being formed of areolar 

 tissue. If we examine a muscle, we find, that the proper muscular 

 fibres become gradually fewer, and at length cease to be perceptible as 

 they approach the tendon at one or other extremity. In this way, the 

 areolar membrane, which surrounds every fibre, becomes freed from 

 the muscular tissue; its divisions approximate, and become closely 

 united and condensed, so as to form the cord or tendon, which, of 

 course, holds a relation to each fibre of the muscle; and when they all 

 contract, the whole force is exerted upon it. The microscopic obser- 

 vations of Mr. Bowman exhibited to him, that the component fibres of 

 the tendinous structure are arranged with great regularity, parallel to 



Fig. 156. 



Attachment of Tendon to Muscular Fibre, in Skate. (Bowman.) 



each other, and are attached to the end of the sarcolemma, which termi- 

 nates abruptly, as in Figs. 148 & 156; which shows the attachment of 

 the tendon to the muscular fibre in the skate. Dr. Leidy 1 observed that 

 the filaments of areolar tissue, which form the sheaths of the muscular 

 fasciculi, proceed, for the most part, in a diagonally crossing manner 

 around the fasciculi, occasionally passing in between the fibres and 

 intermingling with fine filaments of elastic tissue which exist in this 

 situation. The sheaths are also connected together by filaments from 

 them, which pursue the same diagonally crossing course. The fila- 

 ments of the areolar sheaths become more or less straight at the extre- 



1 Proceedings of the Academy of Natural Sciences of Philadelphia, vol. iv., No. 6, 1848; 

 and Quain's Anatomy, by Quain & Sharpey, Amer. edit., by Leidy, i. 319, Philadelphia, 

 1849. ' 



