THE BONE. 



1097 



it is of a red color, and contains, in 100 parts, 75 of water and 25 of solid matter 

 consisting of cell-globulin, nucleo-proteid, extractives, salts, and only a small pro- 

 portion of fat. The red marrow consists of a small quantity of connective tissue, 

 blood-vessels, and numerous cells (Fig. 624), some few of which are fat-cells, but 

 the great majority roundish nucleated cells, the true " marrow-cells " of Kolliker. 

 These marrow-cells proper resemble in appearance lymphoid corpuscles, and like 

 them are amoeboid. Among them may be seen smaller cells, which possess a slightly 

 pinkish hue ; these are the erytliroblasts, from which, as we have seen, the red 

 corpuscles of the adult are derived, and which may be regarded as descendants 

 of the nucleated colored corpuscles of the embryo. 



FIG. K!4- Cells of red marrow of the guinea-pig. (Schafer.) a-d. Myeloplaques. e-i. Marrow-cells proper. 

 j-t. fcrythroblasts some m process of division. 



Griant-cells (myelo-plaques, osteoclasts), large, multinucleated, protoplasmic 

 masses, are also to be found in both sorts of adult marrow, but more particularly 

 in red marrow. They were believed by Kolliker to be concerned in the absorption 

 of bone matrix, and hence the name which he gave to them osteoclasts. They 

 excavate small shallow pits or cavities, which are named Hoivship's laeunce, in 

 which they are found lying. 



Vessels of Bone. The blood-vessels of bone are very numerous. Those of the 

 compact tissue are derived from a close and dense network of vessels ramifying in 

 the periosteum. From this membrane vessels pass into the minute orifices in the 

 compact tissue, running through the canals which traverse its substance. The 

 cancellous tissue is supplied in a similar way, but by a less numerous set of larger 

 vessels, which, perforating the outer compact tissue, are distributed to the cavities 

 of the spongy portion of the bone. In the long bones numerous apertures may 

 be seen at the ends near the articular surfaces, some of which give passage to the 

 arteries of the larger set of vessels referred to ; but the most numerous and largest 

 apertures are for the veins of the cancellous tissue, which run separately from the 

 arteries. The medullary canal in the shafts of the long bones is supplied by one 

 large artery (or sometimes more), which enters the bone at the nutrient foramen 

 (situated in most cases near the centre of the shaft), and perforates obliquely the 

 compact structure. The medullary or nutrient artery, usually accompanied by 

 one or two veins, sends branches upward and downward to supply the medullary 

 membrane, which lines the central cavity and the adjoining canals. The ramifica- 

 tions of this vessel anastomose with the arteries both of the cancellous and com- 

 pact tissues. In most of the flat, and in many of the short spongy bones, one 

 or more large apertures are observed, which transmit, to the central parts of the 

 bone, vessels corresponding to the medullary arteries and veins. The veins emerge 

 from the long bones in three places (Kolliker) : (1) by one or two large veins, 



