756 
ME. W. K. PAEKEE ON THE STETJCTUEE AND 
There will be now a necessity for some modification of the nomenclature used in the 
former paper, both with regard to the tissues and the various morphological regions ; 
for in both these departments of my work I trust there has been some extension of 
knowledge, as well as rectification of former errors. 
The ossific process, than which nothing is more confusing to the morphologist, has 
of late received a more definite nomenclature (see ‘ On the Shoulder-girdle and Sternum,’ 
Ray Soc. 1868, p. 4) ; the new terms will be used here. These are: — (1) “ ectostosis,” 
for that tract of osseous deposit which is formed between the perichondrium and the 
cartilaginous mass ; (2) “ endostosis,” for that deposit which takes place primarily in the 
intercellular substance of hyaline cartilage, or between the cells of simple cartilage ; and 
(3) “ parostosis,” for all ossifications of mere fibrous tracts. In the paper ‘On the 
Shoulder-girdle ’ (p. 10) I have spoken of a modification of the growth-process in the 
Warm-blooded Classes, which, until fairly understood, cost me much perplexing thought ; 
this is where a parosteal patch of bony matter grafts itself upon a cartilaginous plate, 
setting up, first, an ectosteal deposit close upon the cartilage-mass, and then an 
endosteal process between the cells themselves. In this case we have the coexistence of 
the three types of “ ostosis ” to form a single osseous centre ; and this state of things, 
so different from what is seen in the Cold-blooded Classes, and by no means to be con- 
founded with after-coalescence, must be looked upon as a very important metamorphic 
modification in the skeleton of the higher types*. 
As far as I can see at present, an explanation of this deliquescence, as it were, of the 
histological process in the formation of bone will greatly smooth the difficulties that have 
hitherto stood in the way of the homological part of this science ; it will thus be seen that 
nothing is more unsafe than hasty decision upon representative parts in the various types. 
There is much to be done in the study of cartilage with regard to morphological 
regions, and their comparison in the various types ; for in some cases differentiation and 
chondrification are synchronous, and, in a sense, synonymous; whilst in others the 
fission of the cartilage does not take place until it is thoroughly consistent and even 
dense. This after-splitting may be perfect, or more or less imperfect ; in the latter case 
a cartilaginous plate becomes notched in some instances, and fenestrate in others (see 
‘ Shoulder-girdle and Sternum,’ p. 4). 
But as hyaline cartilage is merely to be considered a consolidated primordial cell- 
mass, and a very fast-growing tissue also, it is not surprising to find it running riot over a 
large number of morphological territories (op. cit. p. 4) : this takes place to the 
greatest extent in the lowest and most generalized types, which, however large (even 
gigantic) they may become, are nevertheless mere embryos throughout life, in respect 
of their morphological development. 
The sharp distinction between the skull and the vertebrae is well seen in this — that 
* In the Amphibia no definite line can he drawn between parastoses and ectostoses, and the most typical 
endosteal deposit is merely an ossification of that part of the fibrous laminae which immediately encloses the 
cartilage. 
