314 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



elongated sub-cylindrical bodies, sometimes grouped together in a reticular man- 

 ner; these bodies, being the first rudiments of the muscular fibres, not merely 



Fig. 103. 



Fig. 104. 



Muscular Fibres from fcetal pectoralis : 

 A, from Calf at two months ; B, from Human 

 foetus of nine months. 



Mass of Muscular Fibres from 

 the pectoralis major of the Hu- 

 man foetus, at nine months. These 

 fibres have been immersed in a 

 solution of tartaric acid; and 

 their numerous corpuscles turn- 

 ed in various directions, some pre- 

 senting nucleoli, are shown. 



in* the heart, but also in the other striated muscles, are designated, by M. Le- 

 bert, "myogenic cells." Between the seventh and eighth days, the "organo- 

 plastic globules" undergo a considerable diminution, and the muscular substance 

 presents a more complete development. A longitudinal striation shows itself 

 in the contents of the cylinders, which seems partly due to the grouping of the 

 granular particles of which these contents consist; the transverse striations do 

 not show themselves until some time afterwards. Between the seventh and 

 ninth days, the myogenic cells become more regularly cylindrical and their ex- 

 tremities more rounded ; the tendinous fasciculi then begin to be visible, inclos- 

 ing the lower part of the cylinders, without having as yet any direct relation of 

 continuity with them. The interior of the cylinders becomes more regularly 

 striated in the direction of its length; and between the tenth and twelfth days, 

 the transverse striae appear on the surface, and multiply rapidly, becoming at 

 the same time more and more regular. The " organo-plastic globules," which 

 at first separated the primitive cylinders, gradually disappear; the cylinders 

 approach one another ; and before the end of embryonic life, they are found to be 

 grouped into fasciculi. M. Lebert has further shown, that different members of 

 the animal kingdom permanently exhibit the Muscular fibre in the different 

 phases of development here described; 1 and it appears probable that the smooth 

 muscular fibre-cells of Prof. Kolliker are to be regarded as the original " myo- 

 genic cells," within which no secondary formation has taken place. There seems 

 every probability that the nuclei of the parent-cells continue to act as " centres 

 of nutrition" during the whole life of each fibre ; furnishing the germs from 

 which the minute secondary cells, that compose the fibrillae, are developed as they 

 are required. The diameter of the Muscular fibre of the foetus is not above one- 

 third of that which it possesses in the adult ; and as the size of their ultimate 

 particles is the same in both cases, their number must be greatly multiplied 

 during the growth of the structure. But we shall find reason to believe, that 

 a decay is continually taking place in the component cells, with a rapidity pro- 



1 "Annales des Sci. Nat.," Mars, 1850. 



