THE MUSCULAR SYSTEM. 276 



moreover, they become distinctly visible to the naked eye, 

 that their elementary constituents can be made out, at this 

 time presenting the appearance of long parallel bands with 

 elongated nuclei, which, as the observations of Schwann and 

 myself (§ 24) on very young animals show, arc formed by 

 the coalescence of fusiform cells. As early as the fourth mouth 

 they may be distinctly recognised as primitive fasciculi, which 

 are wavy, and present, at intervals, elongated nuclei 0*0035 — 

 0-006'" long, and 0-0016'" broad, but are as yet without dis- 

 tinct fibrils, and not more than 0-0012 — „. ,„„ 

 . . . Fig. 107. 

 00016'" wide. From this period up to the 



end of foetal life, the fasciculi gradually 

 increase in width, so that in the new-born 

 infant they measure 0-002 — 0-0025'"; 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'", 

 it is obvious, that the fasciculi of the tendons 

 are continually acquiring an increase in thick- 

 ness from their first origin, so that their pro- 

 portional 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, more- 

 over, appear, that subsequent 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 erroneous, as is 

 readily shown by the examination of the mammalian and 

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



Fig. 107. From the tendo Achillis of a new-born child, x 250 diam., treated with 

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



