22 DR. G. THIN. 



sides. The terminal fibres at opposite poles are accordingly 

 often visible Avhen the others are not seen. In the present 

 case one of the terminal fibres is necessarily cut off" when the 

 section is made. It is Avorthy of remark that although when 

 covered by the cartilage the cells in question show no special 

 disposition to assume an elongated form, they invariably do 

 so when the cavity has been laid open. 



The drawings of Bubnoff and Heitzmann the author believes 

 to represent spaces that exist between the layers of cartilage. 

 He is thus in accord Avith BubnofFmore than with Heitzmann. 

 Heitzmann believes that the appearances which he has re- 

 produced are those of a cell and its protoplasmic processes. 

 The author interprets the appearances shown in Heitzmann's 

 own drawings as representing stellate spaces, and sees nothing 

 in them that he can interpret as cell-processes ; being thus 

 at one Avith him as regards the fact observed, but differing 

 from him in regard to its interpretation. 



In that part of cartilage Avhich adjoins the demarcating 

 line characterised as the zone of absorption Avhen bone is 

 being formed there is a preliminary absorption Avhich ex- 

 tends further into the cartilage than is generally supposed, 

 although, not being permeable to blood-\'essels, it is not so 

 evident. For some distance into the cartilage the separation 

 of the layers AA-hich compose the Avails of the spaces increases 

 in extent until the intervening narroAv communication 

 betAveen tAvo spaces is swamped, and Avhat was originally tAvo 

 spaces with their intervening communication becomes one 

 large space. A section through cartilage at this point, if 

 stained in carmine or picrocarminate, shows the nucleus of 

 each of the cells which lay in the original spaces lying at 

 opposite ends of the ncAvly formed large space, an appear- 

 ance which without more ado has been deemed conclusiA-e 

 proof of the division of one cell into two. A further separa- 

 tion of the laminae permits the entrance of ncAv blood-vessels 

 into the space, and in the language usually employed the 

 "capsule" or " cell'' is said to be "opened." 



In this series of changes the relation of cause and effect 

 between the two processes of increased entrance of lymph- 

 fluid and thinning of the walls of the laminae has not been 

 determined by direct observation. 



The author acknowledges his obligation to Dr. Ewart for 

 executing the folloAving draAvings, and other valuable assist- 

 ance rendered him Avhilst engaged in the studies AA'hich have 

 served as a basis for this paper. 



August, 1875. 



