CHAP. VII.] 



DEVELOPMENT OF MUSCLE. 



157 



Fig. 43. 



isolate a muscular fibre, with the tendinous fibrillae pertaining to it, 

 either in mammalia or birds ; but this may be occasionally accom- 

 plished in fishes, and in certain muscles of insects. In these exam- 

 ples, the minute detachment of 

 the fibrous tissue may be seen to 

 pass, and to become attached to 

 the truncated extremity of the 

 fibre. The fibre ends by a per- 

 fect disc, and with the whole 

 surface of this disc the tendon is 

 connected and continuous. The 

 sarcolemma ceases abruptly at the 



Circumference of the terminal disc, Attachment of tendon to an elementary fibre 



, , ,, e , from the Skate : On bringing deeper and deeper 



and here SOme Small part Ot tne portions of the specimen into focus, along the line 



, . . , -, of union, a. a., fresh tendinous wavy filaments and 



tendmOUS material appears tO DC striated muscular parts came into view together. 



. . T .. -r .-, t. Tendon, m. Muscle. 



joined to it. In other cases, 



where the muscle is fixed obliquely to a membranous surface, each 

 fibre is obliquely truncated at its extremity, at an angle determined 

 by the inclination of its axis ; instances of which may be seen 

 among the Crustacea, and elsewhere. 



The researches of Valentin and Schwann have shewn that a 

 muscle consists, in the earliest stage, of a mass of nucleated cells, 

 which first arrange themselves in a linear series, with more or less 

 regularity, and then unite to constitute the elementary fibres. As 

 this process of the union of the cells is going forward, a deposit of 



Fig. 44. 



Stages of the development of striped muscular fibre. 



a. ArrangciiH-nt of tin-, primitive cells in a linear series. After Schwann. 



b. The cells united. The nuclei separated, and some broken up; longitudinal lines becoming appa- 

 rent. From a foetal calf three inches long. 



c. d. Transverse stripes apparent. In c, the nuclei are internal, and bulge the fibre. In d, they are 

 prominent on the surface. From a foetal calf of two months old. 



e. Transverse stripes, fully formed and dark ; nuclei disappearing from view. From the human infant 

 at birth. 



/. Elementary fibre from the adult, treated with acid; shewing the nuclei. Magnified about 300 

 diameters. 



