OKGANS OF THE BODY. 



57; 



ties. In the long bones it is met with as a yellow mass, found under 

 the microscope to be made up of scanty bundles of connective-tissue 

 interspersed with fat-cells (fig. 552, d, e). Chemical analysis shows it to 

 be composed of neutral fats to the amount of 96 per cent., according to 

 Berzelius (comp. 122 and 147). In the epiphyses, on the contrary, 

 and in flat and short bones, the medulla is a reddish or red mass of 

 soft consistence, made up usually of bundles of connective-tissue similar 

 to those of the last variety (but in smaller quantity), with an ever- 

 decreasing number of fat-cells containing, on the other hand, numerous 

 small contractile lymphoid elements, with granular contents and distinct 

 nuclei. These latter, 0-0090-0-0113 mm. in diameter, are identical with 

 the cells figuring in plate 552, b, from the medulla of an infant. Like 

 them, they were formerly supposed to be 

 descendants of the cartilage medullarv 

 cells ( 147). 



On the surface also of the yellow variety 

 of medulla, cells of this kind are to be met 

 with here and there. 



An interesting point, in regard to these 

 lymphoid cells of the medulla of bones, 

 has recently been noticed by Neuman and 

 Bizzozero in the osseous tissues of man and 

 other mammalia. This is the transfor- 

 mation of the former into red blood cor- 

 puscles, reminding us of the formation of 

 embryonic blood. The possibility of im- 

 migration of these into the vessels of the 

 medulla is suggested. 



Another kind of element is also to be 

 found in the medulla of bones, and, more- 

 over, at all periods of life, namely, large isolated membraneless multi- 

 nuclear cells, known as myeloplaxes (p. 258). According to Berzelius, red 

 medullary substance from the diploe contains 75*5 per cent, of water, 

 traces 2 4 '5 of solid constituents, protein compounds, and salts, but merely 

 of fatty matters. 



7. Muscular Apparatus. 



290. 



The structures we are now about to consider briefly have been already 

 described in the second portion of our work in dealing with muscular tissue 

 ( 162-173). The structure of the tendons formed the subject of 134, 

 belonging as they do to the connective-tissues, among which the fascias 

 also are included. In 109 the fact was also mentioned, that at those 

 points where tendons are inserted into bone, deposits of cartilage cells are 

 not unfrequently met with between the bundles of fibres, of which the 

 structure is chiefly composed, thus giving rise to a kind of fibro-cartilage. 

 That the same cartilaginous tissue may be developed in the interior of 

 tendons was also remarked in the same place. Here, then, we have the 

 source of se.satnoid cartilages, whose place again may be taken by analogous 

 osseous formations known as sesamoid bones. 



The blood-vessels of the tendons can be only found with great difficulty, 

 nay, further, small sinews are entirely destitute of them, and are supplied 

 entirely by a wide-meshed network contained in the connective-tissue in 



Fig. 552. Medullary cells of cartilage, a, 

 from the humerus of a human foetus at 

 five months; 6, from the same bone of 

 an infant shortly after birth ; c, stellate 

 and fusiform cells from the first; a", 

 formation of the fat-cella of the marrow; 

 e, a cell filled with oil 



