198 NOTES AND MEMORANDA. 



connection with extranuclear minute filaments^ which permeate 

 as networks the substance of the cell itself. In the ciliated cells 

 above named the cilia extend into the cell-substance and appear 

 to identify themselves with those filaments. 



[Heitzmann described a similar network of minute fibrils 

 within the substance of the cell-protoplasm]. — E. K. 



On the Postembryonal Growth of Bone.i — By Professor 

 ScHWALBE. Professor Schwalbe finds that in man, beginning with 

 the ninth month or end of first year of life till the fourth or fifth 

 year, the periosteum deposits only minimal quantities of bone 

 substance, so that in tubular bones (femur, tibia, humerus) no 

 appreciable growth in thickness takes place. As the medul- 

 lary cavity continues to expand during the just named period it 

 follows tliat the compact substance is iJdnner at a later (four 

 years) than at a younger stage (three years). Calculation on the 

 volume of the compact substance showed that the total volume of 

 the cortex of diaphysis (formed from the periosteum) is smaller 

 in individuals of four years than in those of three, a physiological 

 absorption of bone is therefore proved beyond doubt. As regards 

 the microscopic appearance of growing bone, Professor Schwalbe 

 finds the following : in the first period, after birth till about the 

 sixth mouth, the tubular bone grows from the periosteum after 

 the embryonal mode, and possesses the peculiar structure 

 common to embryonal bone — viz. that of a trellis-work (v. 

 Ebner). Beginning with the sixth month a distension takes 

 place in all vascular spaces, which become converted into wide 

 Haversian spaces, owing to an absorption of bone-substance. 

 This second period may be called the stage of osteoporosis. The 

 osteoporosis extends as a rule only on the inner half or the inner 

 two thirds of the shaft. Before this, however, is completed, the 

 first formation of lamellar bone takes place in the innermost parts 

 that had been subjected to the osteoporosis. This formation is due 

 to the medulla. Gradually all parts of the shaft (including the 

 peripheral portion in which meanwhile Haversian spaces have 

 been formed) become provided with lamellar, i.e. Haversian 

 systems of bone-substance. This represents a third stage, viz. 

 the stage of formation of the Haversian lamella. Through all 

 this time, however, the tubular bone has not increased in thick- 

 ness, and it follows, therefore, that up to the end of the fourth 

 year the periosteum takes no part in the formation of lamellar 

 bone-substance. 



Beginning with the fourth year the periosteum produces 

 ground-lamella3. In these the Haversian spaces are formed 



^ ' Sitzungsber. der Jenaischen Gesellschaft f. Med. und Naturwiss.,' 

 6th July, 1877. 



