256 



SPECIAL HISTOLOGY. 



nuclei, which, as the observations of Schwann and myself ( 24) on very 

 young animals show, are formed by the coalescence of fusiform cells. 

 As early as the fourth month they may be distinctly recognized as primi- 

 tive fasciculi, which are wavy, and present, at intervals, elongated nuclei 

 0-0035-0-006 of a line long, and 0-0016 of a line broad, but are as yet 

 without distinct fibrils, and not more than 0-0012-0-0016 of a line wide. 

 Fig. 107. From this period up to the end of foetal life, the fasci- 



culi gradually increase in width, so that in the new- 

 born infant they measure 0-002-0-0025 of a line; at 

 the same time their fibrils are developed, as are also 

 fine elastic filaments among the fasciculi, from special 

 fusiform formative cells (vide 23). If these fasciculi 

 be compared with those of the adult, measuring 0-006 

 -0-008 of a line, it is obvious, that the fasciculi of the 

 tendons are continually acquiring an increase in thick- 

 ness from their first origin, so that their proportional 

 sizes in the four months' foetus, the new-born child, and 

 the adult, are about as 1 : 1, 8 : 6 ; and, also, that in 

 every case the growth of the tendons must in a great 

 measure be referred to the increased thickness and 

 elongation of their fasciculi. It would, moreover, appear, that subse- 

 quent to the primary rudiments of the tendons, new fasciculi continue 

 to be added during foetal life. 



Some controversial opinions are still entertained with respect to the 

 development of the muscular fibres. Reichert and Hoist maintain that 

 each fibril is the product of a single cell, and regard it as the equivalent 

 of the smooth muscular fibre, or contractile fibre-cell. This view is er- 

 roneous, as is readily shown by the examination of the mammalian and 

 human embryo. Leydig's declaration, quite recently, in its favor 

 (Beitr. p. 78), is explained by his having confounded the peculiar secon- 

 dary muscular fasciculi in the plagiostomous fishes with the primitive 

 fasciculi of the higher Vertebrata. In the Batrachia, according to 

 Lebert and Remak, in the development of the muscles, elongated simple 

 cells, with self-multiplying nuclei, are found, the contents of which cells 

 undergo a metamorphosis similar to that occurring in the elongated 

 muscular tubules formed of numerous cells, which, according to my ob- 

 servations, also exist in these animals. The contractile part of the mus- 

 cular fibre, whether it be transversely striped or not, and whether it 

 presents fibrils or not, is generally developed from without to within, in 

 the sarcolernma, forming a sort of tube w.hich does not become solid till 

 afterwards ; less frequently it appears as a more solid cord on one side 



FIG. 107. From the tendo ^chillis of a new-born child, magnified 250 diameters, and 

 treated with acetic acid, in order to show the formation of fine elastic fibres. 



