SEROUS AND SYNOVIAL MEMBRANES. 



517 



gress towards the trochanter of the femur, is a 

 convenient one for examination. On making 

 a thin section parallel to the osseous surface, 

 it is found that the bands of the white fibrous 

 element which constitute the periosteum are 

 considerably changed where they line the 

 bursae. They are much less wavy than usual, 

 and, at the same time, have become much 

 more brittle and transparent. Besides be- 

 coming more linear, the markings have altered 

 in another respect, viz. they are much less 

 frequent, and are placed at more regular dis- 

 tances. The ordinary epithelium which else- 

 where lines the cavity has disappeared, and, 

 in its stead, we recognise a great number of 

 cells irregularly scattered over the surface of 

 the specimen j although even now one may 

 perhaps trace an approach to a longitudinal 

 arrangement in their greater proximity in this 

 direction. These cells, in respect of their 

 solidity, their somewhat angular shape, their 

 colourless transparency, and refractility, greatly 

 resemble those seen in articular cartilage. 

 They are, in fact, cartilage corpuscles. But 

 although exactly on the surface these cells are 

 somewhat flattened, and scattered with com- 

 parative irregularity, this appearance by no 

 means extends any depth in the tissue. A 

 slight alteration of the focus shows that, im- 

 mediately beneath the surface, corpuscles are 

 not only less numerous, but also assume a dis- 

 tinctly linear arrangement; and form somewhat 

 interrupted longitudinal rows, which chiefly 

 occupy the interstices of the altered bands 

 of white fibrous tissue. The corpuscles them- 

 selves are here more angular and elongated. 

 By further altering the focus, and obtaining 

 a deeper view, the lines marking these sur- 

 faces are seen to be crossed by others ; and a 

 closer inspection reveals the existence of two 

 strata : one, the superficial layer just ex- 

 amined, of which the lines are in the direction 

 of motion, or transverse to this border of the 

 ischium ; and another deeper layer, which 

 lies at right angles to the preceding, and im- 

 mediately covers the bone. In the latter, the 

 same corpuscles exist, but in rather fewer 

 numbers. The application of acetic acid slowly 

 swells and dissolves the intercellular sub- 

 stance, and renders the cells more distinct, 

 but does not deepen their colour. After a 

 considerable interval of time, it attacks the 

 corpuscles themselves, and renders them in- 

 visible ; apparently more from its effect on 

 their relations to the refractility of the 

 surrounding substance, than from a real so- 

 lution. 



In like manner, the under surface of the 

 tendon offers^a similar cellular structure, and 

 a corresponding, but much less considerable, 

 modification of the fibrous tissue itself. But 

 this change, which, on the surface, is so well 

 marked, gradually diminishes as one examines 

 successive and deeper horizontal sections ; 

 and, finally, at a certain depth, the intercellu- 

 lar substance altogether loses its cartilaginous 

 characters, the cells themselves vanish, and 

 the tendon completely resumes its ordinary 

 structure. 



The crossing of two strata at right angles 

 to each other, which is witnessed in the 

 modified periosteum, is a frequent anatomical 

 peculiarity of the original tissue, and not 

 essential to the modification. And something 

 very similar is seen in the tendon. The 

 tendinous bundles to which the several mus- 

 cular fibres are attached, are successively 

 received into the border of the oblique ten- 

 don j and very frequently, in joining it, a 



Fig. 397. 



a b 



Under or Bursal Surface of Obturator Interims Ten- 

 don. From the Cat. 



a, superficial stratum ; b, deeper layer lying at an 

 oblique angle to the preceding. (Magnified about 

 180 diameters.) 



certain proportion of their fibres swerve 

 aside from its track, scatter themselves, 

 and strengthen the cord as a whole, by cross- 

 ing its surface at a varying angle, and form- 

 ing a thin stratum superficial to it. Where 

 the tendon assumes the peculiarities just al- 

 luded to, the markings and corpuscles of this 

 superficial layer are seen decussating those of 

 the larger and deeper mass which take the 

 direction of the tendon. This crossing of 

 two strata is indicated inj%. 397. 



The chief differences between the cells on 

 the surface and those at a greater depth have 

 been already indicated ; viz., that the former 

 are more numerous, flatter, and more oval. 

 But the shapes and appearances of the deeper 

 layer deserve further consideration, since 

 they present the phenomena of a fissiparous 

 genesis of cells, which the upper stratum does 

 not ; so that it is perhaps difficult to avoid 

 attributing the increase of numbers and alter- 

 ation of shape which is seen near the surface 

 to the gradual advance of the multiplied cor- 

 puscles in that direction. The stages of the 

 process are the same as may be observed in 

 other tissues. An elongation of the nucleus 

 is followed by an hour-glass constriction of its 

 middle ; a dark line across the corpuscle then 

 testifies to the fission of both cell and nucleus ; 

 and, finally, the two new cells separate, and 

 their walls surround the nucleus at a more 

 equal distance in every part. Most of these 

 steps may be observed in^g. 397. 



L L 3 



