6o 



HISTOLOGY. 



cross sections. In longitudinal sections they appear as in Fig. 63. Veins 

 pass back from the marrow, through the Haversian canals, emerging 

 through the periosteum. It will be noticed that in longitudinal sections 

 the lamellar systems are scarcely distinguishable. On the marrow side, the 

 endosteum forms a thin fibrous layer containing occasional osteoblasts and 

 osteoclasts. The marrow will be described with the blood-forming organs. 



Hyaline 

 cartilage. 



Perichondra^ 

 bone. 



FIG. 65. FROM A DORSO-PALMAR LONGITUDINAL SECTION OF A PHALANX OP THE LITTLE 

 FINGER OF A HUMAN FETUS Six MONTHS OLD. X 60. 



Preparations from washed and dried bones show only the calcareous 

 framework. Sections made by sawing show macroscopically an arrange- 

 ment of the spongy bone in arches and trusses to resist compression. 

 Microscopic sections are made by grinding thin sawed slices until they 

 become translucent, and mounting them so that the lacunae and canaliculi 

 remain full of air. Since the air is refractive it appears black. Thus the 

 canaliculi are clearly demonstrated, as in Fig. 64. They extend from one 



