THE MUSCULAR SYSTEM. 241 



fibres. Both of these kinds of sacs are lined, on the inner surface, to- 

 gether with the parts contained in or otherwise bounding them, but only 

 in places, with an epithelium, consisting for the most part of a simple layer 

 of nucleated polygonal cells 0-004-0-007 of a line in diameter. The parts 

 which are bare of epithelium, are : many portions of the mucous sheaths, 

 and the tendons lying in them, and certain spots of the bursce mucosce 

 themselves, which are distinguishable by their dull lustre and yellowish 

 aspect, and which occur especially in those situations where the tendons 

 and parts surrounding them are exposed to a greater degree of pressure. 

 The common flexor sheath of the fingers is lined throughout with epi- 

 thelium; and the same may be said of the mucous bursse, in which it is 

 only certain loop-like ligaments, which beyond the limits of the bursae 

 still surround the tendons, that do not present any cellular covering, as 

 is the case, occasionally, in the subscapularis poplitceus, &c. 



All these bare places, which are uncovered by epithelium, invariably 

 exhibit, almost throughout, the nature of fibre-cartilages, the dense con- 

 nective tissue of which they are composed, and which for the most part 

 is furnished with but few elastic elements, containing a greater or less, 

 often a very considerable number of cartilage-cells" (Fig. 99), amongst 

 which, the most frequent are rounded 

 cells, with a dark contour, although by 

 no means with thick walls, measuring 

 0-006-0-012 of a line, with a roundish 

 nucleus of 0-003 of a line, and clear fluid, 

 with or without some minute, opaque fatty granules. Besides these, 

 there are, moreover, elongated cells, with one or two nuclei ; round, 

 thin-walled cells, containing 1, 2-20 secondary cells, with thick walls, 

 and dark contours ; the mother-cells measuring as much as 0-02-0-03 of 

 a line ; and lastly, elongated cells, with concentric deposits, inclosing a 

 nucleus, or nucleated secondary cell. In the tendons, the simpler forms 

 of cells almost exclusively occur, and the cells, although frequently ex- 

 tremely numerous, are for the most part isolated, or, at most, disposed 

 in rows or groups of 2-6, which are contained in the connective tissue, 

 both superficially and more deeply. In most cases, the common con- 

 nective tissue alternates with one more resembling fibro-cartilage, so 

 that the tendon, on a transverse section, presents a speckled, white and 

 yellowish aspect; or it maybe, that the outer surface only of the tendon 

 contains cartilage, the deeper portions retaining their usual condition. 

 Where the deposition of the cartilage cells is most abundant, the tendons 

 become thickened, or even studded, as it were, with distinct, fibro-carti- 

 laginous masses (peroneus longus, tib. posticus). In the mucous bursse 

 and the other parts above named, the cartilage cells are placed, not un- 



FIG. 100. Cartilage-cells from the vaginal ligaments surrounding the tendons of the 

 poplit&us, magnified 350 diameters: a, cell with one; 6, with two nuclei; c, cell with one; 

 rf, with two secondary cells, both of which have rather thick contents. 



16 



