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 trabecule 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 
