CLARKEj ON STRIPED MUSCULAR FIBRE. 225 



variety unite nearly end to end by means of short but broad 

 granular processes or tails^ which overlap each other and 

 coalesce, as in the case of the muscular fibre represented at 

 fig. 5 d. But those of a more pyriform shape, arranging them- 

 selves in a line, with their corresponding ends turned in the 

 same direction, are attached to each other by slender filamen- 

 tous processes proceeding from their points, each of which 

 rests on the same side against the shoulder of the next suc- 

 ceeding nucleus, so that the entire series appears to be con- 

 nected on that side by a continuous fibre. This arrangement, 

 however, is less frequently seen than the other. 



In the heart of the chick, between the third and fourth 

 days of incubation, the fusiform, nucleated bodies are much 

 more numerous and more distinctly marked than in the volun- 

 tary muscular tissue. When a portion of either of the ventricles 

 is dissected under the microscope by means of fine needles, it 

 is found to consist — 1, of a granular, semifluid blastema; 2, of 

 free nuclei, both round and oval, containing one or two globu- 

 lar nucleoli ; and^3, of the same kind of nuclei, either partially 

 or wholly surrounded each by a granular mass of more or less 

 definite outline and shape (see fig. 7). Sometimes only a 

 small conical projection of granular substance grows from one 

 side of a nucleus, and tapers into a fibre of variable length. 

 By a similar growth on its opposite side a fusiform body 

 begins to make its appearance, and is sometimes prolonged 

 until it assumes, to a certain extent, the form of a nucleated 

 fibre. Pyriform, oval, and circular bodies are produced by 

 the same process, according to the direction which it takes. 

 Sometimes the granular mass enveloping the nucleus is not 

 definitely circumscribed (see fig. 7) ; in many cases its surface 

 is smooth and its outline well defined, while in others it is 

 partially or wholly surrounded by a slightly condensed layer, 

 which presents more or less the appearance of a separate 

 envelope or border, as at a. In their normal position these 

 elementary bodies are arranged side by side with considerable 

 regularity, as represented at fig. 7 b, and by their union and 

 growth constitute bundles of muscular fibres. 



Towards the end of the sixth, or at the early part of the 

 seventh, day of incubation, a striking difference or modifica- 

 tion may be observed in the process of development of the 

 muscular fibres of the trunk. The free nuclei are still 

 exceedingly abundant, and the nucleated fibres already 

 described are also present in great numbers. But in ad- 

 dition to these a multitude of others, somewhat different 

 in their form and mode of development, begin to make 

 their appearance. These new structures originate in a 



