NORMAL HISTOLOGY. 



more or less delicacy will be exposed ; these are the perforating 

 fibres of Sharpey, and represent periosteal fibres which have failed 

 to undergo calcification ; of these Kolliker recognizes two kinds 

 those entirely soft and uncalcified, the most numerous and, at the 

 same time, the smallest ; and those partly calcified and of larger size, 

 which, in fact, are bundles of fibrous tissue. Sharpey 's fibres are 

 most numerous in the superficial lamellae of spongy bones, although 

 found in the interstitial lamellae of other bones, pinning together the 

 lamellae which they transfix. The perforating fibres, being derived 

 from the periosteum, never occur in the lamellae of the Haversian 

 systems, since the latter, it will be found, are not directly produced 

 by the periosteum, but as secondary deposits. 



Additional elements of the bone-matrix are the elastic fibres, 

 which are found in the outer fundamental lamellae, as well as occasion- 

 ally in the deeper interstitial lamellae; these elastic fibres are generally 

 associated with the uncalcified Sharpey' s fibres ; not infrequently the 

 elastic fibres are contained within the uncalcified bundles of fibrous 

 tissue composing the large perforating fibres. 



Marrow of Bone. The cavities within bones, as well as the 

 elaborate intercommunicating nutrient channels extending through- 

 out the osseous tissue, are filled with the highly vascular marrow, 

 which genetically is an extension of the osteogenetic layer of the 

 periosteum, since the primary marrow is a direct ingrowth and ex- 

 tension of this latter tissue. The marrow of all bones in very young 

 animals is red in color; after a certain time, however, that con- 

 tained within the shafts of the tubular and the spaces of some 



other bones assumes a lighter 

 tint, finally becoming of a 

 straw color, owing to the 

 accumulation of fat within 

 the marrow-cells. Depend- 

 ing upon this difference, two 

 varieties the red marrow 



and the yellow marrow 

 are recognized : it is to be 

 remembered that the red 

 marrow is genetically the 

 older and represents the 

 primary condition. 



elements of the red marrow comprise a delicate connective- 

 reticulum supporting a rich vascular distribution, composed of 

 aru.-rioles breaking up into numerous capillaries, which, in turn, give 

 place to venous radicles of large size and extremely thin walls. The 



FIG. 58. 



Elements of the bone- marrow: g t multinucleated 

 giant-cell, or myeloplax ; m, marrow-cells ; n, granule- 

 cell. 



