STRUCTURE OF MUSCLE. 



171 



Pis*. 102.* 



both surfaces, and containing, somewhere near the centre, one, two, or 

 Jiree minute dots or granules." Occasionally they are seen to present ir- 

 regularities of form, which Mr. Bowman is inclined to regard as accidental. 

 They are situated between, and are connected with the fibrils, and are 

 distributed in pretty equal numbers through the fibre. These corpuscles 

 are the nuclei of the nucleated cells from which the 

 muscular fibre was originally developed. From ob- 

 serving, however, that their "absolute number is far 

 greater in the adult than in the foetus, while their 

 number, relatively to the bulk of the fasciculi, at these 

 two epochs, remains nearly the same," Mr. Bowman 

 regards it as certain, that " during development, and 

 subsequently, a further and successive deposit of cor- 

 puscles" takes place. The corpuscles are brought 

 into view only when the muscular fibre is acted upon 

 by a solution of " one of the milder acids, as the citric." 

 According to my own investigations,! the ultimate 

 fibril of animal life is cylindrical when isolated, and 

 probably polygonal from pressure when forming part 

 of an ultimate fibre or fasciculus. It measures in 

 diameter -^J^ of an inch, and is composed of a suc- 

 cession of cells connected by their flat surfaces. The 

 cells are filled with a transparent substance, which I 

 have termed myoline. The myoline differs in density 

 in different cells, and from this circumstance bestows 

 a peculiarity of character on certain of the cells ; for 

 example, when a fibril in its passive state is examined, 

 there will be seen a series of dark oblong bodies se- 

 parated by light spaces of equal length ; now the dark 

 bodies are each composed of a pair of cells contain- 



Fig. 103.t 



Jb C 



1 1 ! 



i i 



i B 



ing the densest form of myoline, and are hence highly refractive while the 

 transparent spaces are constituted by a pair of cells containing a more 

 fluid myoline. When the fibrils are collected together so as to form an 

 ultimate fibre or fasciculus, the appearance of the cell is altered ; those 

 which look dark in the single fibril, that is, the most refractive, being 



* Mass of ultimate fibres from the pectoralis major of the human foetus, at nine 

 months. These fibres have been immersed in a solution of tartaric acid, and their 

 'numerous corpuscles, turned in various directions, some presenting nucleoli," are 

 shown. From Mr. Bowman's paper. 



j- These were made on dissections of fresh human muscle, prepared with great care 

 by Mr. Lealand, partner of the eminent optician, Mr. Powell. 



$ Structure of the ultimate muscular fibril and fibre of animal life. 



A. An ultimate muscular fibril in the state of partial contraction. 



B. A similar fibril in the state of ordinary relaxation. This fibril measured - L_ 

 of an inch in diameter. 



c. A similar fibril put upon the stretch, and measuring -^^ of an in ch in diameter. 



D. Plan of a portion of an ultimate fibre, showing the manner in which the transverse 

 tries are produced by the collocation of the fibrils. 



Nos. 1, 1. The pair of highly-refractive cells; they form the dark parts of the single 

 fibrils, but the bright parts of the fibre D. In the stretched fibril c, each cell has the 

 appearance of being double. 2, 2. The pair of less refractive cells, light in the single 

 fibrils, but forming the shaded stria in D. The transverse septum between these cells 

 is very conspicuous ; and in c two other septa are seen to exist, making the number of 

 transparent cells four. In a, the tier of cells immediately above the dark tier is partia.ly 

 illumined from the obliquity of the light. 



