THE CONNECTIVE TISSUES. 



49 



FIG. 56. 



In dried bone the spaces are filled with air, the lacunae and cana- 

 liculi consequently appearing dark and sharply defined when viewed 

 by transmitted light. The lacunae, sometimes improperly called 

 "bone-cells," in dried preparations are empty, or, at most, contain 

 the remains of the soft, protoplasmic bodies, the true bone-cells, 

 which during life partially fill the spaces ; these, like the cells of other 

 dense connective tissues, lie within the lymph-spaces of the ground- 

 matrix. In sections of young, well-stained, decalci- 

 fied fresh bone, after the usual manipulations, the 

 bone-corpuscles are seen as nucleated, stellate, 

 protoplasmic bodies, whose processes extend into 

 the canaliculi ; in adult and old bones, however, the 

 cells become reduced in size and very inconspicuous. 

 The lacunae being lenticular, they present different 

 figures according to the direction in which they are 

 sectioned : cut transversely, they appear as short, 

 narrow ovals ; opened longitudinally, but not parallel 

 to the lamellae, they are seen as long, narrow, elliptical figures ; while 

 when cut longitudinally, and at the same time parallel to the lamellae, 

 they present a broad, oval surface, sometimes almost circular ; the 

 canaliculi, extending in all planes, appear much the same in all 

 sections. 



The periosteum, an envelope of vascular connective tissue, 

 closely invests the outer surface of all bones except the articular 



A bone-cell lying 

 within the lacuna of 

 the osseous matrix : 

 decalcified and 

 stained. 



FIG. 57. 



' 



facets. This important 

 structure is composed of 

 two portions an outer, 

 dense, protective, fibrous 

 layer, and an inner, much 

 looser stratum, rich in 

 cells and blood-vessels, 

 which, from its intimate 

 relations to the formation 

 of bone, is known as 

 the osteogenetic layer. 

 This latter contains within 

 its meshes numerous 

 round or spindle cells, 

 many of which later be- 

 come bone-forming ele- 

 ments the osteoblasts. 



If a decalcified bone be sectioned parallel to the superficial lamellae, 

 especially if these be of a spongy bone, or if the outer lamellae be 

 forcibly torn off, a number of transverse or perpendicular fibres of 



4 



Fragments torn from the surface of a decalcified bon : A, 

 surface ; B, oblique view ; s, Sharpey's perforating fibres ; 

 /, the lacunae. 



