STRUCTURE OF MUSCULAR TISSUE. 



313 



few sensory are blended with them. We see this most clearly in cases, in which 

 the motor and sensory trunks supplying the muscles are distinct; as in the 



Fig. 102. "..* 



Form of the terminating loops of the Nerves in the Muscles. 



muscles of the orbit. The non-striated muscles are very sparingly supplied with 

 nerves; and these are derived (for the most part, if not entirely), from the Sym- 

 pathetic system, rather than from the Cerebro-Spinal. 



310. The development of striated Muscular fibre commences, according to 

 Schwann and Valentin, in the development of a linearly-arranged series of cefls 

 from nuclei lying in the midst of a soft blastema. At the points of contact be- 

 tween the cells, the partitions disappear ; and thus a continuous tube is formed, 

 which seems to become the myolemma of the fibre. The nuclei of the original 

 cells, however, still remain; and besides these, the tube may be seen to contain 

 a number of granular particles, which gradually (according to the observation of 

 Dr. Sharpey 1 ) come to present a somewhat regular disposition in transverse lines 

 between the nuclei. The full development of the transverse striae, which indi- 

 cates the complete evolution of the contained nbrillae within the myolemma, does 

 not take place until subsequently. For some time, the nuclei continue to be 

 very apparent, in consequence of their projection from the edges of the fibre, 

 and of the smallness of its diameter (Fig. 103) ; but as the fibre increases in 

 size, they become more embedded in its substance; and in the muscular fibre of 

 the adult, their presence can only be made evident by treating the fibre with 

 weak acids (such as the citric or tartaric) which renders the nuclei more opaque, 

 whilst the surrounding structure becomes more transparent. (Fig. 104). They 

 are usually numerous in proportion to the size of the fibre. The development 

 of the striated fibre has more recently been carefully studied by M. Lebert in 

 the Heart of the Chick. 3 The rhythmical contractions of this organ become very 

 manifest and regular towards the 36th hour of incubation : nevertheless, it is at 

 this time composed of nothing else than l( organo-plastic globules" or elemen- 

 tary cells embedded in a granular blastema. Between the fourth and fifth days 

 of incubation are seen in the midst of the mass of globular particles, certain 



mities. But although there is no doubt as to the frequency of that arrangement in cold- 

 blooded Vertebrata, as well as in many Invertebrated animals, yet, from the researches of 

 Prof. Kolliker, it seems certain that the looped arrangement prevails in the muscles of 

 Man and of other Mammalia ; and that the subdivision of the nerve-fibres, with the ter- 

 mination of the fibres in free extremities, if it take place at all, is quite exceptional. (See 

 his " Mikroskopische Anatomie," band ii. pp. 238-247.) 



1 See his Introduction to " Quain's Elements of Anatomy," vol. i. p. 324, Am. Ed. 



3 "Annales des Sci. Nat.," Juin, 1849. 



