64 CONNECTIVE TISSUES. 



be used just as other tissues hardened in chromic acid (see 

 Chap. VI.). 



For the study of the periosteum and of the compact bony 

 substance, i.e., of its lamella? and lacuna?, with the cells con- 

 tained in them, sections of the long bones of man are very 

 suitable. The spongy substance can be best examined in the 

 metacarpal and metatarsal bones and in the phalanges of 

 children, or in those of rabbits or rats. Very instructive sec- 

 tions may also be obtained from the tibia of the frog, showing 

 the compact substance of the bone, as well as the pigment 

 cells, fat cells, medullary cells, and bloodvessels of the marrow. 

 Medullary tissue can be also advantageously studied in the 

 tongue bone of birds. The whole tongue is hardened in 

 chromic acid solution, after which sections are made through 

 the posterior part of the tongue, so as to pass through the 

 bone in question. Sections of bone prepared as above afford 

 evidence that the cells which occupy the lacunre are strictly 

 analogous to the branched cells of other connective tissues, 

 so that the system of lacunas and canaliculi, seen in prepara- 

 tions of dried bone, corresponds entirely with the system of 

 canaliculi (Saftcandlchen) seen in silver preparations of the 

 cornea, serous membranes, etc. And it may even be shown 

 in preparations of the flat bones of the skull, or of the tongue 

 bone of birds, that the cells are not only in continuity ex- 

 ternally with those of the periosteum (which, although really 

 branched, look spindle-shaped in section), but internally, i.e., 

 towards the medulla, with cells which are also more or less 

 branched, but are arranged so regularly and so close together 

 against the bony surface, that the}' resemble an endothelial 

 lining. In the flat bones of the skull of human embryos, the 

 same arrangement presents itself with great distinctness the 

 cells, which line the medullary cavities, being then called 

 osteoblasts. 



The medullary tissue of bone is rich in bloodvessels and in 

 cellular elements. The former are best seen in injected prepa- 

 rations (see Part II., Chapter VI.). After the injected part 

 has been one or two days in alcohol, the bone must be freed 

 from surrounding tissues, and steeped in chromic acid with 

 the addition of hydrochloric acid, as before. The medullary 

 cells, which differ in size and in the distinctness of their granu- 

 lation, may be examined in the fresh condition on the warm 

 stage, for the demonstration of their amoeboid movements, in 

 the manner several times described previous!}'. In chromic 

 acid preparations, the individual medullary cells, as well as 

 the fat cells, retain their form and aspect. 



Development of Bone-tissue. For the study of the 

 development of bony tissue (whether from cartilage or from 

 fibrous tissue, as in the flat bones of the skull) the human 



