THE OSTEOLOGY OF AMIURUS CATUS. 309 



formation, producing osseous trabecule 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 

 premaxillse 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 trabecular 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 1 

 is now proved to be imperfect, and consequently also "Vrolik's" 2 classi- 

 fication of bone formation into perichonrostotisch and enchondrosto- 

 tisch. Walther 3 from his observations on the pike, classifies the 

 various kinds of bone thus : — 



!1. Cementknochen (primare Deckknochen). 

 2. Bindegewebsknochen (secundare Deckknochen). 

 3. Perichondralknochen (centrifugal wachsend). 



Knorpelknochen i L Perichondral (centripetal wachsend). 



( 2. Enchondral (Bildung von Knochenkernen). 



Goldi, again, in a very recent paper, objects to Walther 's distinc- 

 tion between centrifugal and centripetal perichondral bones and 

 classifies thus : — 



T u ,, , ( 1. Cementknochen. 



1. idautknochen { 



( 2. Bindegewebsknochen. 



II. Perichondrale j 1. Exo-peri chondral (centrifugal wachsend.) 

 Knochen ( 2. Endo-perichondral (centripetal wachsend), 



and refers to a third group endrochondral bones, i. e., those formed 

 from a centre of ossification in the centre of the cartilage. 



1 Oegenbaur— Elements of comparative anatomy. 



2 Vrolik — loc. cit. 



8 Walthtr —Die Entw. d. Deckknochen am Kopf-skelet des Hechtes (Esox lucius). Jen. 

 Zeit. Ed. XVI., 1882. 



