270 THE H RSE. 



ally present rough surfaces for this purpose, and are also closely 

 incorporated with the periosteum. This union is so strong, that 

 it very rarely gives way; and when extreme violence is used, 

 either the bone itself breaks, or the tendon snaps in its middle. 

 Tendons are non-elastic. 



To THE NAKED EYE, an ordinary muscle appears to be com- 

 posed of a number of small bundles of fibres, arranged in parallel 

 lines, and connected by a fine membrane. These bundles may 

 still further be separated into what seem at first to be elementary 

 fibres ; but when placed in the microscope, they are found to be 

 themselves made up of finer fibres united into fasciculi by delicate 

 filaments. These ultimate fibrillae are polyhedral in section, ac- 

 cording to the observations of Mr. Bowman, so as to pack closely 

 together, and are variable in size in different classes and genera of 

 animals. They also differ in appearance, one class presenting 

 stripes while the other is without them. The former includes all 

 the muscles whose movements are under the control of the will as 

 well as those of the heart, and some of the fibres of the oesophagus, 

 while the latter is composed of the muscles investing the stomach, 

 intestines, bladder, &c., which are comprehended under the gene- 

 ral term involuntary. 



THE SARCOLEMMA is the name given by Mr. 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 specific structure, but some- 

 times it presents an aspect as if there was an interweaving of fila- 

 ments 



WHEN A FIBRILLA of striated muscle is examined under the 

 microso pe of a high magnifying power, it is seen to present a 

 bear 3 . appearance as if made up of a linear aggregation of dis- 

 t : , cells, alternately light and dark When the fibrilla is 



axed, each cell is longer than it is broad ; but, during the 



\\*g^ ^ 'he muscle, it assumes the opposite dimensions, the increase 



rtii&'ftf ; A ~r being always in r.-oportion to tb diminution of 



tl the contraction takes ^lace~M$ -^^uustance becomes 



uier than before, but the brlk ..mains the same, the mass 

 merely gaining in thickness wha it has lost in length. The 

 application of certain stimulating n f ents will produce the contraction 

 for a certain period aftev life i.s destroyed, varying according to 

 the vitality of the aiiim il < ; .mented upon and the nature cf the 

 indiv' : %1 mup Tlrs called irritability in the striated 



as-iSv whic 1 *bit pow ful contractions, alternating with re- 

 'xi' -w in the Involuntary muscles a more steady, per- 

 mit L> lerate contraction is met with, to which the name 

 of tr ;>t^ as e^i ' -i. 



PURE 'U^ui.iR IRE appears to be identical in composition 



