STKIATED MUSCULAK FIBEE. 



399 



5. Tubes readily breaking into fibrillae; or precisely like the 

 striated fibre in the Mammalia, as in certain muscles of insects. 



6. Lastly, simple isolated cells, containing a transversely striated 

 substance which fills the whole cell or only forms a thin layer upon 

 its internal surface. These exist also, according to Kolliker, in the 

 endocardium of the Euminantia ; constituting the peculiar cartila- 

 ginous striae first observed by Purkinje. 



Development of Striated Muscular Fibre. 



The myolemma is formed originally of nucleated cells, first co- 

 alescing and then becoming absorbed where they come into con- 

 tact, so as to form tubes closed at both extremities. Subsequently 

 the original homogeneous contents of the formative cells are re- 

 placed by the fibrillse, and thus the development of the fibre is com- 

 pleted. In many cases the layer of the contents next the myolem- 

 ma alone gives place to the myoline ; while the central part still 

 appears like a canal within the fibrils. It has been seen that this 

 is the permanent form of the striated fibre in some insects. After 

 the fibrillge are developed, and before birth, the nuclei disappear, 

 and, with the exception of being smaller, the fibres present the same 

 appearance as in the adult. 



More particularly in the embryo at the end of the second 

 month, the fibres have the form of elongated bands T2 ^<r of an inch 

 broad, with nodular enlargements at different points where elon- 

 gated nuclei are situated. (Fig. 253.) These bands have either a 



Fig. 253. 



Fig. 254. 



Fig. 253. Stages of the development of striated muscular fibre. 1. Arrangement of the primitive 

 cells in a linear series, after Schwann. 2. The cells united ; the nuclei separated and some broken 

 up, longitudinal series becoming apparent from a foetal calf three inches long. 3, 4. Transverse 

 strire apparent. In (3) the nuclei are internal, and bulge the fibre. In (4) they are apparently on 

 the surface from a foetal calf, two months old. 5. Transverse stripes, fully formed and dark; 

 nuclei disappearing from view from the new-born infant. 



Fig. 234. Muscular fibre, from the adult, treated with acid showing the nuclei. (Magnified about 

 300 diameters.) 



