140 E. A. SCHAFER. 



periosteal bone is quite different in structural appearance and in 

 its behaviour to many staining reagents from the subjacent car- 

 tilage-bone, beyond which it is prolonged at either end of the 

 shaft for a little distance over the surface of the cartilage, so 

 that the formation of the periosteal membrane-bone always 

 slightly precedes the extension of the calcification of the cartilage 

 within. 



This advanced part of the ossifying periosteum generally lies 

 embedded in a groove on the surface of the cartilage (Plate VII, 

 fig. 2) — the " encoche d'ossification " of Ranvier ; and when 

 the ossification has progressed nearly to the end of the bone, 

 the advanced part becomes very much thickened and extends 

 deeply into the cartilaginous head. The appearance presented 

 is as if the periosteal thickening were eating its way into the 

 cartilage which is becoming absorbed before it ; but it is pos- 

 sible that it may be produced by the lateral expansion of the 

 cartilaginous head over the end of the ossifying periosteal 

 tube. 



Whatever may be the precise mode of its production the 

 appearance is very striking, as exhibited in the longitudinal 

 section of a bone the shaft of which is far advanced in the 

 process of ossification like the one represented in fig. 3. The 

 groove formed by the advancing periosteal ossification is repre- 

 sented more highly magnified in fig. 3. It is here seen that the 

 tissue which occupies the groove is sharply marked off and 

 totally distinct from the cartilage itself. It includes no car- 

 tilage-cells at any part, but is chiefly occupied by rounded or 

 irregular granular cells (osteoblasts) amongst which are seen 

 a number of straight tapering fibres, which can be traced below 

 from the already formed periosteal bone. The tissue in question 

 is obviously not fibro-cartilage, as described and figured by 

 Ranvier.^ It encroaches on the cartilage and may possibly 

 be formed at the expense of the cartilage, but even if this be so, 

 there is no trace of the latter remaining in it. A few of the 

 fibres above mentioned may apparently be traced for a short 

 distance into the matrix of the cartilage, but these are excep- 

 tional, and are mostly met with in the superficial parts near the 

 fiibrous perichondrium, the fibres of which, it is well known, are 

 generally traceable for a short distance into the subjacent 

 cartilage. 



Respecting the delicate straight fibres which are seen in this 

 tissue, it has been observed that they are directly continued 

 from the bony matter which is already formed under the perios 

 teum. IVom this circumstance, as well as on account of their 

 general appearance and their osteoblast surroundings, it is im- 

 ' 'Traits Teclinique,' fig. 159, p. 450. 



