226 



SPECIAL HISTOLOGY. 



FiL'. 93. 



facility in either ; and in the second place, that, in the thoracic muscles 

 of insects, the individual fibrils may be very distinctly and beautifully 

 seen (Fig. 93) in the muscles, when quite fresh. When we consider the 

 great similarity between the muscles of insects and of 

 the higher animals, in every essential particular, this 

 fact appears to me to be of a striking nature. I am, 

 therefore, from this and the other reasons assigned, 

 thoroughly convinced of the existence of fibrils during 

 life, and believe that, where they do not so readily 

 admit of being isolated, as in man and many animals, 

 they are connected by a homogeneous, tenacious (albu- 

 minous), interstitial substance, which is very evident in 

 a transverse section, and in fact so firmly, that, under 

 certain circumstances, transverse rupture of the fasciculi 

 may take place, that is to say, in the direction of the 

 thinner spaces of the fibrils ; as also occurs in other 

 fibres ; for instance, in the elastic tissue, smooth muscles, 

 and even in the corneous cells (internal root-sheath and 

 cortex of the hair). With all this, it must not be sup- 

 posed that fibrils exist in all muscular fibres of animals, 

 either themselves striped or corresponding to the striped fibres here 

 described. The study of development and of comparative anatomy 

 much rather teaches that the muscular fibre occurs in various conditions, 

 and, particularly, that it frequently exhibits more homogeneous contents, 

 with or without transverse striation, and without fibrils. This, however, 

 of course, affords no ground for the assumption of such a condition in 

 man and the mammalia also ; and although such muscular fibres, in 

 certain animals, readily break up into transverse segments (Leydig), 

 still, it is not thereby proved that in the higher animals a similar 

 division of the contents is to be regarded as natural, and that into 

 fibrils as artificially produced. 



The diameter of the primitive fasciculi varies, not inconsiderably, in 

 different muscles, or in one and the same muscle. Henle (who is fol- 

 lowed by Gerlach), at an earlier period, assigned to them a diameter 

 of 0-005-0'006, and at most of 0-017 of a line; but more lately 

 (Stadelmann, " Sectiones transversse"), has declared that these measure- 

 ments are not universally correct. I will here give some particulars 

 upon which the measurements stated above, in the text, are founded. 

 In a female, the fasciculi of the sacro-lumhalis measured 0-016-0-028, 

 the majority 0"020-0-022 of a line; in the pectoralis major, 0"01-0*03, 

 most of them 0-02 of a line ; deltoid, O-OlG-0-026, the majority 0-02- 

 0-022 of a line; in the masseter, 0-006-0-02, the majority 0-01-0-018 



Fig. 93. — Primitive fibres from a quite recent transversely-striated muscle of a Bug ; 

 magnified 350 diameters. 



