GENERAL HISTOLOGY. 1 05 



and of the marrow-cavity and form a mantle of concen- 

 tric layers around the marrow-cavity. Into this ground- 

 work enter the Haversian canals with their lamellae, de- 

 stroying and superseding the fundamental lamellae coming 

 in their way. The Haversian lamellae are concentri- 

 cally arranged around the lumen of the Haversian canals 

 just as are the fundamental lamellae around the marrow- 

 cavity. 



Formation of Bone. The stratification of bone is 

 caused by its mode of origin. Where the bone borders 

 upon the Haversian canals, the marrow-cavity, and the 

 periosteum, there is transiently or permanently an epithe- 

 lial-like layer of cells, ' ' o stcoblasts, " which secrete on 

 their surface the bone-substance. Certain cells in the 

 fundamental substance participate in this secretion, and 

 here give rise to the bone-corpuscles, which are distin- 

 guished from the cartilage-cells by their numerous pro- 

 cesses ramifying through the fundamental substance. The 

 processes of a bone-corpuscle branch, and unite with 

 the neighboring cells through fusion of the processes; 

 their arrangement is most beautifully seen in dried bone, 

 because here the cavities and the canals of the funda- 

 mental substance are filled with air. A special modifi- 

 cation of bony tissue the substance of fish-scales, and of 

 the teeth, called also ivory or substantia cburnca, should 

 be mentioned. 



Blood and Lymph, here treated in connection with 

 the connective substances, are, in reality, not tissues at all, 

 but nutritive fluids. Two kinds of nutritive fluids occur 

 in the vertebrates, red blood and the colorless, weakly 

 opalescent, or cloudy white lymph. In the blood of man 

 and the vertebrates, we should distinguish particularly the 

 fluid and the organized constituents. The blood-fluid or 

 blood-plasvia is, apart from inorganic constituents, specially 

 rich in proteids; after the removal of the blood from the 

 blood-vessels a part of these separate by coagulation and 

 form the blood-clot, made up of fibrin, leaving a fluid poor 

 in proteids, the blood-serum. The organized constituents, 



