230 



SPECIAL HISTOLOGY. 



Fia-. 94. 



These secondary muscular fasciculi, as thej are termed, are, each of 

 them, enclosed by a special envelop of connective tissue, and, several 

 together, united by stronger membranes into tertiary fasciculi, which, 

 lastly, in a greater or less number, unite and constitute the separate 

 bellies of the muscle, or muscles themselves. If the muscular fasciculi 

 are placed in the same plane, they constitute the membranous or fiat 

 muscles ; and when disposed in a thick bundle, the elongated or columnar 

 muscles. The muscles consequently are aggregations of numerous, 



larger and smaller secondary 

 and tertiary fasciculi, the 

 sheaths or perimysium of 

 which constitute a connected 

 system, in which that por- 

 tion which surrounds the en- 

 tire muscle, as the perimy- 

 sium externum or muscular 

 sheath {vagina muscularis\ 

 is to be distinguished from 

 the more internal elements 

 immediately surroundino; the 

 larger and smaller fasciculi and the muscular fibres — the perimysium 

 internum. The thickness of the secondary fasciculi varies from g to ^ 

 a line ; that of the tertiary and still larger bundles, which are most 

 evident in muscles with coarse fibres [glutceus maximus, deltoideus), is 

 so various, and the division of the muscle in these more remote constitu- 

 ents is so arbitrary, that there is nothing specially to be said with re- 

 spect to them. 



The muscular sheaths or envelops, perimysium, composed of con- 

 nective tissue, which are for the double purpose of conveying the vessels 

 and nerves of the muscles, and of connecting the muscular fibres and 

 supporting them when in action, vary in thickness according to the 

 greater or less size of the groups of fasciculi surrounded by them. 

 They are always, however, delicate, dull-Avhite, non-glistening tunics, 

 consisting of common connective tissue, and minute, isolated or anasto- 

 mosing elastic fibres, of at most 0-001 of a line in thickness, the latter 

 occurring in greater number, especially in the perimysium externum, 

 which may, consequently, very properly and conveniently, be regarded 

 as a semi-elastic membrane, and its function estimated in accordance 

 "with this structure. In all muscles, especially in those of a more lax 

 construction, a certain number of adipose cells of the usual kind (fre- 



FiG. 94. — Transverse section from the rectus capitis anticus major of Man, magnified 350 

 diameters: a, external perimysium; b, perimysium internum; c, primitive fasciculus and 

 secondary muscular fasciculus. 



