228 CLARKE, ON STRIPED MUSCULAR FIBRE. 



have now assumed the form of nucleated cylinders of a more 

 peculiar character, and arranged side by side with much 

 regularity (fig. 12 a). These fibres differ from each other 

 considerably in diameter, and each of them varies in the same 

 respect at difi"erent parts of its course. 



At their widest portions, which are nearly uniformly 

 cylindrical, their walls are of considerable thickness, and on 

 each side have the aspect of a broad band or contour, enclosing 

 an axis of delicately granular substance and a series of nuclei. 

 The nuclei assume a variety of shapes and positions. They 

 are round or oval, pyriform or crescentic, and turned with 

 their longer diameters either more or less transverse or 

 parallel to the course of the fibre. Sometimes they are 

 crowded closely together, sometimes the interval between 

 them is variable, while in a great number of instances they 

 lie at moderate and nearly equal distances from each other, 

 and occupy the whole axial breadth of the fibre, which is 

 then constricted between each pair in such a manner as to 

 resemble a jointed or knotted cane (see fig. 12 a). Some of 

 them are quite on the surface, the convexity of which is 

 occasionally embraced by a nucleus of a crescentic form 

 (fig. 12 5). 



After a certain course these fibres are frequently seen to 

 change their character, in consequence of a further develop- 

 ment. They gradually diminish in diameter to a variable 

 extent, and assume a more cylindrical shape. At the point 

 where this change is taking place the granular axis tapers 

 off; the fibre, contracting in the same proportion, acquires 

 a uniform structure throughout its entire thickness, and the 

 lateral contours disappear (fig. 12 6). The nuclei also, as if 

 by pressure, become frequently much more elongated longi- 

 tudinally, and raise the surface in the form of alternate 

 nodes. At the same time some of the fibres exhibit indica- 

 tions of longitudinal fibrillation and even of transverse strise. 

 Sometimes a fibre tapers for a considerable length without 

 any other alteration of structure, in consequence of the 

 absence of nuclei, which allows the walls to approach each 

 other and the granular substance to form a narrower axis ; 

 and in such instances the walls now and then are seen to 

 have resolved themselves into fibrillse, and these again into 

 granules. (See fig. 12 c.) 



By the fifteenth day of incubation the fibres lose entirely 

 their plane structure, and become wholly resolved throughout 

 their thickness into bundles of fibrillae (fig. 13 «). These 

 fibrillse, however, are not perfectly parallel, but overlie each 

 other here and there in a loose kind of way, and, in conse- 



