THE EVIDENCE OF THE SKELETON 135 



definite account of how the new cartilages are formed. Bujor, 

 Kaensche, and Schaffer all profess to give a more or less definite 

 account of their formation, and the one striking impression left on 

 the mind of the reader is how their descriptions vary. In one 

 point only are they agreed, and in that I also agree with them, viz. 

 the manner in which the new cranial walls are formed. Schaffer 

 describes the process as the invasion of chondroblasts into the 

 homogeneous fibrous tissue of the cranial walls. Such chondro- 

 blasts not only form the cartilaginous framework, but also assimilate 

 the fibrous tissue which they invade, so that finally all that remains 

 of the original fibrous matrix in which the cartilage was formed are 

 these lines of cement-substance between the groups of cartilage 

 cells, which, containing some basophil material, are marked out, as 

 already mentioned (Fig. 57). 



We may therefore conclude, from the investigation of Ammoccetes, 

 that the front part of the basi-cranial skeleton arose as two trabecular 

 bars, to which muscles were attached, situated bilaterally with respect 

 to the central nervous system. These bars were composed of tendinous 

 material with a gelatinous rather than a mucoid substratum, in which 

 nests of cartilage- cells were formed, the cartilaginous material formed 

 by these cells being of the hard variety, not staining with thionin, 

 and staining yellow with picro-carmine, etc. By the increase of such 

 nests and the assimilation of the intermediate fibrous material, the 

 original fibro-cartilage was converted into the close-set semi-hyaline 

 cartilage of the trabecular and auditory capsules, in which the fibrous 

 material still marks out by its staining-reaction the limits of the 

 cell-clusters. 



Such I gather to be Schaffer's conclusions, and they are certainly 

 borne out by my own and Miss Alcock's observations. As far as 

 we have had an opportunity of observing at present, the first process 

 at transformation appears to consist of the invasion of the fibrous 

 tissue of the cranial wall by groups of cells which form nests of cells 

 between the fibrous strands. These nests of cells form round them- 

 selves capsular material, and thus form cell-territories of cartilage, 

 which squeeze out and assimilate the surrounding fibrous tissue, until 

 at last all that remains of the original fibrous matrix is the lines of 

 cement-substance which mark out the limits of the various cell-groups. 



At present I am inclined to think that both soft and hard cartilage 

 originate in a very similar manner, viz. by the formation of capsular 



