230 CLARKE, ON STRIPED MUSCULAR FIBRE. 



fusiform bodies, and these be arranged in tbe same imbricate 

 manner, it is easy to perceive that their opposite ends by 

 their coalescence will form a border on their opposite sides. 

 Sometimes a fibre bifurcates here and there to enclose an 

 oval or pyriform nucleus, as shown at d, and sometimes the 

 branches are connected beyond the nucleus by an expansion 

 of condensed blastema in which still finer fibres may be 

 observed."^ Frequently the nuclei are disposed in irregular 

 groups around the ' fibres, to which they are cemented 

 (fig. 14 e). 



As development advances, fibres of different diameters are 

 produced in the way already described. Fig. 16 a represents 

 one of the smaller kind in progress of formation. The 

 majority, however, are of much larger diameter than this, 

 but differ from it only in having a thicker coating of the 

 condensed material, which, when seen on each side, presents 

 the appearance of bands enclosing a granular and nucleated 

 axis (fig. 16 c). That these fibres are more or less cylin- 

 drical, and sometimes entirely surrounded by this condensed 

 coating, is rendered probable by the fact that the apparent 

 bands are seen always and only at their sides, just as in 

 nerve-fibres the medullary sheath or white substance is seen 

 only on each side of the axis- cylinder ; but if any doubt exist 

 on the subject it may be set at rest by examining a trans- 

 verse section of a long muscle, the cut ends of which show 

 that the fibres are more or less cylindrical, with an axis 

 sometimes entirely surrounded by a thick, tubular sheath. 

 Fig. 17 represents a transverse section of fibres from the 

 leg of the foetal sheep, two inches long. The substance of 

 this coating or sheath is easily injured, broken up, or dis- 

 placed, even by careful manipulation; and this tendency, 

 under exactly similar circumstances, is greater in mammalia 

 than in the chick. Sometimes it separates into small pieces 

 or coarse granules, which are more or less round, square, 

 cylindrical or discoid, and are very distinctly seen along the 

 sides of the fibres. When these pieces become confusedly 

 heaped together with the nuclei which the sheath contained, 

 without destroying the cylindrical shape of the fibres, these 

 fibres might be supposed to be in the first stage of develop- 

 ment by means of an irregular aggregation of their elements. 

 But that this condition is a breaking up, and not a process of 

 development, any one may convince himself by a sufficiently 



* When the muscular tissue is subjected to the action of even a weak 

 solution of chromic acid, these appearances are very common. The fibres 

 become connected by a kind of network, which seems to be caused by tlie 

 action of the acid on the blastema, and must be looked upon with caution. 



