302 



PLAIN OR UNSTRIPED MUSCULAR TISSUE. 



various stages of development have been described in muscles at all stages of growth, 

 and also in the adult condition, so that it has been conjectured that new muscular 

 fibres may be formed in this way even after the development of the muscle is com- 

 pleted. Nothing is known of the manner in which absorption of pre-existing fibres 

 is effected to make room for the newly-formed fibres ; if, indeed, such change occurs 

 at all. 



According to Mayer, many of the structures which have been described, under the name 

 sarcoplasts and muscle-spindles, as fibres in course of development, are in reality fibres under- 

 going degeneration. Kerschner, on the other hand, from their relatively large nerve supply, 

 believes the muscle-spindles to be sensory end-organs. 



Regeneration. It was formerly thought that after removal by the knife or by 

 disease striated muscular tissue is not regenerated, but that any breach of continuity 

 which may occur in a muscle is filled up by a growth of connective tissue. It would 

 appear, however, that the breach is, after a certain lapse of time, bridged across by 

 muscular substance, but how the new muscular tissue is formed is not fully understood, 



PLAIN OR UNSTRIPED MUSCULAR TISSUE. 



This is made up of cells, named contractile fibre-cells, which were first dis- 

 tinguished as the true elements of the tissue by Kolliker. The cells may form 



fibrous bundles, and strata, 

 or may be less regularly 

 arranged, and the tissue occurs 

 either almost pure or mixed 

 . with other tissues in varying 



proportion. The cells are of an 

 elongated fusiform shape (figs, 

 346 and 347), usually pointed 

 at the ends. They are generally 

 prismatic in transverse section, 

 but are sometimes more flat- 

 tened. The cells vary greatly 

 in length according to the part 

 or organ in which they are 

 found. Some occur which are 

 cleft or forked at one or both 

 Fig. 346. MUSCULAR FIBRE-CELLS FROM ends. Their substance is finely 



(E. A. S.) faint longitudinal fibrillation. 



A, a complete cell, showing the nucleus It i g doubly refracting. Each 

 with intranuclear network, and the longitu- cell has a nucleus (a, a), rarely 

 dinal fibrillation of the cell-substance, with ^ whioh is alwavs 

 protoplasm between the fibrils. ne > Wm 



B, a cell broken in the process of isola- elongated and either oval or 



tion ; the delicate enveloping membrane rod-shaped. Towards each end 

 projects at the broken end a little beyond /? ,-, ,1 



the substance of the cell (B is from a draw- f the nucleus the substance of 

 ing by Mr. R. Boxall). the cell usually contains a few 



distinct granules arranged in 

 linear series. 



The nucleus shows the usual 

 structure, having an intranu- 

 clear network (fig. 34G, A). 

 The involuntary fibre-cells pos- 

 sess an exceedingly delicate homogeneous sheath (fig. 346, B), and like the sarcolemma 

 of voluntary muscular fibres, this sheath is apt to be wrinkled when the fibre is 



Fig. 347. MUSCULAR FIBRE-CELLS FROM 



HUMAN ARTERIES, MAGNIFIED 350 DIA- 

 METERS. (Kolliker. ) 



a, a, nucleus ; I, a cell treated with 

 acetic acid. 



