STRUCTURE OF MUSCLE. 



161 



Fig- 77 t 



its myolemma. The myolemma, or investing sheath of the ultimate 

 fibre is thin, structureless and transparent. 



According to Mr. Bowman * the ' 

 ultimate fibres are polygonal in shape, 

 [fig. 77] from mutual pressure. They 

 are also variable in their size, not 

 merely in different classes andgenera 

 of animals and different sexes, but 

 even in the same muscle. For ex- 

 ample, the average diameter of the 

 ultimate fibre in the human female 

 is 3^-3-, while that of the male is 

 sJrg, the average of both being 

 3^. The largest fibres are met 

 with in fishes, in which animals 

 they average ^ ; the next largest 

 are found in man, while in other 



classes they range in the following order : insects ^-j-g ; reptiles 

 &* ' mammalia ^ ; birds ^fc. 



The ultimate fibrils of animal life, according to Mr. Bowman, are 

 beaded filaments consisting of a regular succession of segments and 

 constrictions, the latter being narrower than the former, and the com- 

 ponent substance probably less dense. 



An ultimate fibre consists of a bundle of these fibrils, which are so 

 disposed that all the segments and all the constrictions correspond, and 

 in this manner give rise to the alternate light and dark lines of the 

 transverse striae. The fibrils are connected together with very dif- 

 ferent degrees of closeness in different animals ; in man they are but 

 slightly adherent, and distinct lon- 

 gitudinal lines of junction may be 

 observed between them ; they also 

 separate very easily when mace- 

 rated for some time. Besides the 

 more usual separation of the ulti- 

 mate fibre into fibrils, it breaks 

 when stretched, into transverse 

 sections [fig. 78,] corresponding 

 with the dark line of the striae, 

 and consequently with the constric- 

 tions of the fibrillae. When this 

 division occurs with the greatest 



* On the Minute structure and Movements of Voluntary Muscle. By Wm. 

 Bowman, Esq. From the Philosophical Transactions for 1840. 



t Transverse section of ultimate fibres of the biceps, copied from the illus- 

 trations to Mr. Bowman's paper. In this figure the polygonal form of the 

 fibres is seen, and their composition of ultimate fibrils. 



J An ultimate fibre, in which the transverse splitting into discs, in the direc- 

 tion of the constrictions of the ultimate fibrils is seen. From Mr. Bowman's 

 paper. 



M 



