THE MUSCULAR SYSTEM. 



223 



Pi?. 89. 



the naked eye, the transversely striated (animal or voluntary) muscular 

 fibres, or primitive fasciculi, are distinguished, especially by their size 

 and the distinctness of their individual parts, from those of most of the 

 striped muscles occurring in other situations (heart, large venous trunks, 

 pharynx, oesophagus, larynx, urethra). With respect to this latter 

 characteristic, it is to be remarked that the sheath of the primitive 

 fasciculus, or the sarcolemma,* in every fasciculus without exception, 

 especially on the addition of water, acetic acid, and alkalies, may at 

 once be recognized as a perfectly structureless, transparent, elastic, 

 smooth membrane, which in man, as in the mam- 

 malia, is distinguished by its delicacy from the same 

 tissue in the lower Vertebrata, and particularly in 

 the naked Amphibia. The muscular or primitive 

 fibrils may, though not without difficulty, be isolated, 

 especially in muscles that have undergone slight 

 maceration, or have been boiled, or immersed in 

 alcohol or chromic acid. In general they are vari- 

 cose, that is to say, present more or less distinct 

 enlargements, at intervals of O'0004-O'OOl of a line ; 

 in consequence of which arrangement, and owing to 

 the circumstance that the thicker and thinner spaces, 

 throughout the entire thickness of the fasciculus, are 

 placed regularly on the same level, the latter for the 

 most part appears to be marked with delicate trans- 

 verse bands. Occasionally, moreover, in addition, a 

 fine parallel striation is evident, or, more rarely, 

 where the enlargements on the fibrils are less appa- 

 rent or quite imperceptible, simply a longitudinal 

 striation. In adults, the fibrils do not enclose any central space or 

 canal (Jacquemin, Skey, Valentin), but, with the addition of a small 

 quantity of a connecting interstitial substance, constitute perfectly 

 compact fasciculi (Fig. 90). On the inner side of the sarcolemma, 



FIG. 89. Primitive fibrils from a primitive fasciculus of the Axolotl (Siredon pisciformis) ; 

 magnified GOO diameters : a, a small fascicular composed of them ; 6, an isolated fibril. 



* [It is greatly to be doubted whether the universality of the occurrence of this structure 

 should be so strongly affirmed. We have been unable to detect it either in the muscular 

 bundles of the heart, or in the great majority of those of the tongue, or in any of the muscles 

 of a seven-months' foetus. In fact, the question of the existence of a sarcolemma as an 

 independent structure very much resembles that of the existence of " fibrils." The sarco- 

 lemma must be considered merely as the outer portion of the transparent, homogeneous 

 matrix, in which the " sarcous elements" are imbedded (vide infra)] and the possibility of 

 raising it up by artificial means, or of observing its optical expression, as a distinct structure, 

 will depend upon the amount to which it is developed relatively to the various elements, 

 and the extent of chemical differentiation which has gone on it as compared with the rest 

 of the matrix. Tits.] 



