THE OSTEOLOGY OF AMIURUS CATUS. 309: 
formation, producing osseous trabeculz which replace the cartilage 
as it becomes absorbed, so that one might justly term the dentary a 
cement bone. 
It has now been shown that membrane-bone, cement-bone, and peri- 
chondral bone can replace each other, that they are identical in 
their histological characters, and also that they are identical in their 
mode of formation. A comparison of the upper portions of the 
premaxille with the frontals shows that the process of bone forma- 
tion is in both cases the same, and similarly a comparison of the 
dentary with the palatine or prootic shows that the centripetal peri- 
chondral method can start and be in relation with cement bone just 
as well as centrifugal perichondral bone ; for in the prootic, palatine, 
etc., a layer of bone is first deposited outside the cartilage and by the 
formation of trabecule in connection with this, and extending out 
into the surrounding connective-tissue, the bone grows in thickness. 
There can be no good reason, then, on histogenetic grounds, for the 
separation of these varieties into different groups. 
The Gegenbaurian distinction of bones into primary and secondary! 
is now proved to be imperfect, and consequently also Vrolik’s? classi- 
fication of bone formation into perichonrostotisch and enchondrosto- 
tisch. Walther® from his observations on the pike, classifies the 
various kinds of bone thus :— 
1. Cementknochen (primire Deckknochen). 
‘ Hautknochen 2 Bindegewebsknochen (secundire Deckknochen), 
3. Perichondralknochen (centrifugal wachsend). 
1. Perichondral (centripetal wachsend). 
2. Enchondral (Bildung von Knochenkernen). 
Knorpelknochen 
Géldi, again, in a very recent paper, objects to Walther’s distinc- 
tion between centrifugal and centripetal perichondral bones and 
classifies thus :— 
Pe eyationochen 1. Cementknochen. 
2. Bindegewebsknochen. 
II. Perichondrale § 1. Exo-perichondral (centrifugal wachsend.) 
Knochen 12. Endo-perichondral (centripetal wachsend), 
and refers to a third group endrochondral bones, 7. e., those formed 
from a centre of ossification in the centre of the cartilage. 
1 Gegenbaur—Elements of comparative anatomy. 
2 Vrolik—toc. cit. 
$ Walther —Die Entw. d. Deckknochen am Kopf-skelet des Hechtes (Zsox lucius). Jen. 
Zeit. Bd. XVI., 1882. 
