667 
of Edinburgh, Session 1879 - 80 . 
Haversian system, indicating the probable occurrence of periods 
of cessation, in the deposition of the systemic lamellae, of some 
duration. 
The situation of the lacunae was found to be almost universally 
in the thickness of a lamella. 
The nature of the lacunar membrane is not elastic. 
Functions of Osteoblasts . — For the ordinary classification of bone 
formation, it seems to me that the following is a subdivision more 
in accordance with observed facts. Bone is produced under con- 
ditions where 
1. There is preformed fibrous tissue, 
2. Where no preformed tissue occurs. 
Subperiosteal bone formation comes under the first, and under 
the second, the production of bone upon cartilage spicules and in 
the excavations for Haversian canals. 
There are situations where bone grows at the expense of tendons 
inserted into them ; the level of ossification is indicated by a regular 
and rapid proliferation of the connective tissue corpuscles, the 
resulting corpuscles becoming lacunar cells and secreting the cal- 
careous matrix, the fibrous tissue of the tendon becoming that of the 
osseous matrix. 
Subperiosteally the fibrous tissue of the osseous matrix is preformed 
as the reticulum of the periosteum. This reticulum is produced by 
connective tissue corpuscles of the periosteum ; other protoplasts 
secrete the interfibrillar calcareous cement. 
From these appearances and others observable upon the spicules of 
cartilage in subepiphysal bone production, it seems justifiable to 
ascribe the production of the fibrillar elements on the one hand, and 
the interfibrillar calcareous cement with lacunar and canalicular 
membranes on the other to two sets of protoplasts, which I would 
designate as “ spinners and plasterers.” 
