256 W. M. Baldwin 



Fig. 8 is of especial significance because it represents in the 

 same muscle fibre the two forms of muscle ending which I have 

 mentioned above, the one in which the fibre is inserted upou on 

 obliquely-plaeed surface, as represented by the instance of the bi- 

 penniform muscles sketched in figs. 4 and 5, and the other where 

 the insertion takes place upon a tendon extremity whose fibrillae 

 pursue the same linear direction as those of the muscle fibrillae. 

 At the same time this particular fibre affords an explanation of the 

 genesis of the sarcolemma eminences or projections to which I 

 have previously referred and figured in Sketches 4 and 10 [Ä], which 

 occur upon the internal surface of the tendon end of the sarco- 

 lemma and afford attachment to the muscle fibrillae. The right side 

 of this Sketch demonsti-ates three cone-sbaped sarcolemma prolonga- 

 tions to each of which a tendon fibril is attached. These fibrils 

 are typical of the arrangement observed in the tadpole tail. That 

 portion of the sarcolemma end upon the left side of the figure, 

 however, is closely applied to the obliquely-plaeed fibrillae of the 

 perichondrium enclosing the cartilage of the developiug rib. The 

 component structures upon this side of the muscle fibre have the 

 same arrangement as was seen in the bipenniform muscles. The 

 arrangement upon the right side is to be regarded accordingly as 

 transitional, since in the adult animal all of the muscle fibrillae 

 are disposed as is shown upon the left side of the figure. This 

 Single muscle fibre, then, represents at once the earlier develop- 

 mental condition and as well the adult condition; therefore, there 

 can be found in it the probable explanation of the origin of those 

 projections of the sarcolemma which are shown in fig. 10 [Ä]. 



In the earlier developmental stagea the muscle fibres terminate 

 in the manner represented in fig. 9 i. e., by a number of cone- 

 shaped sarcolemma processes to each of which a connective tissue 

 fibril is attached. In the course of development as the muscle fibres 

 gradually approach and are applied to their definitive insertion, in 

 such instances where this insertion is upou an obliquely inclined 

 structure, as periosteum or peritendinum, the sarcolemma loses these 

 cone-shaped terminal features. This takes place by a flattening of 

 the apices of these cones and a synchronous fusion of the adjacent 

 walls of neighboring cones. By the flattening of the terminal sarco- 

 lemma a better adhesive surface is presented to the flat surface 

 of the structure affording attachment to the muscle. By the fusion 

 of the adjacent cone-walls is brought about the presence in the 



