;l^98 Egbert Thompson Young, 



the neuro-muscular cells usiialW withdraw themselves to a greater 

 or less extent from the muscles, remaining connected therewith by 

 fibrillae (compare Fig. 43 with Fig. 50). but in some cases they 

 remain close to the muscles (Fig. 59), always, however, connected 

 therewith by fibrillae only. There are usually, probably always, 

 several of these fibrillae forming the neuro-muscular connection, 

 which will be discussed in more detail in the study of the nervous 

 system. The neuro-muscular cells may have a connection with one 

 or more muscles (compare Fig. 50, in which is shown a single 

 muscular connection, with Fig. 45, in which two muscles are seen 

 attached to a single cell). 



The muscles are developed by a grouping together 

 and condensation into a compact bundle of pre-existent 

 parenchyma fibres. This method of development was recognized 

 in a very general way by Leuckaet (1856) and Pintnee (1880). 

 In Fig, 44, such a method of development is clearly shown. For 

 the greater length of this muscle its component fibrillae are so closelj' 

 grouped together as to prevent its resolution into its component 

 parts, but at either end it is plainly evident that the muscle is 

 composed of fibres gathered together from the parenchyma and these 

 in their turn may be resolved into still finer fibrillae.^) Only a 

 single cell is found here sending its fibrillae into the muscle, but it 

 is not uncommon to find more than one connected with a developing 

 muscle. 



Since the muscles anastomose freely with each other, forming 

 in fact a muscular network it may be well to define at this point 

 the term "muscle" as it is used in this discussion. By "muscle" is 

 meant a group of muscular fibrillae bound together so closely in a 

 single strand as to render themselves incapable of resolution under 

 a high magnification. Forming, as they do, a network from the 

 first, one cannot properly speak of the points of termination of any 

 individual muscle. 



If now, the embryonic muscles are composed simply of un- 

 differentiated parenchyma fibrillae gathered together in bundles, how 

 is the transformation from this elementarv condition to that of the 



from the cell body , as the latter becomes separated from the muscles 

 (Fig. 45). 



1) The longitudinal striation of the adult muscle indicates that its 

 component fibrillae retain their individuality tbruout its course. 



