256 SPECIAL HISTOLOGY. 



some fine elastic fibres. The mucous sheaths, on the other 

 hand, in agreement with their double function, which in one 

 respect is that of a mucous bursa, and in another that of 

 ligaments confining the tendon or of tendinous sheaths, present 

 in their thinner parts the structure of bursa mucosae, and in the 

 thicker, an tmrnixed, dense connective tissue, frequently with 

 cells disposed in rows, which pass into elastic fibres. Both of 

 these kinds of sacs are lined, on the inner surface, together 

 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'" 

 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 bursa mucosa 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 epithelium ; and the same may be 

 said of the mucous bursas, in which it is only certain loop-like 

 ligaments, which beyond the limits of the bursse still surround 

 the tendons, that do not present any cellular covering, as is the 

 case, occasionally, in the subscapulars, poplitaus, &c. 



All these bare places, which are uncovered by epithelium, 

 invariably exhibit, almost throughout, the nature of fibro- 

 cartilages, the dense connective tissue of which they are com- 

 posed, and which for the most part is furnished with but few 

 elastic elements, containing a greater or less, often a very con- 

 siderable 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, measur- 

 ing 0-006— 0-01 2'", with a round- 

 ish nucleus of 0003'", 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 



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

 the poplitteus, x 350 diam.: a, cell with one; b. with two nuclei; c, cell with one; 

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



