MEMBRANE AND CARTILAGE BONES 163 



series among the cartilaginous fishes, according as a cartila- 

 ginous skeleton penetrates more and more into this fibrous 

 foundation. In the same way the process of ossification sup- 

 plants the cartilaginous skeleton. So long as the ossifications 

 lie in the skin, as in the sturgeon, they form corneous bones 

 (Hornknochen), but when they lie under the skin, they form 

 true bones, e.g., the bones of the skull in the pike" (p. 374). 



Embryologists soon become aware that a similar distinc- 

 tion between a primitive cartilaginous foundation and a 

 secondary overlying ossification of the skull showed itself in 

 the development of all Vertebrates. Duges, in his RecJiercJies 

 sur I* osteologie et la myologie dcs Batraciens ( 1 834), distinguished 

 between such bones as are formed by direct ossification of 

 the cartilaginous groundwork of the skull, and such as are 

 developed in the periosteal fibrous tissue. 



Reichert in I838 1 noted that several of the skull bones in 

 Amphibia are formed without the intermediary of cartilage, 

 such as the nasals, the maxillaries and the lacrymals. 

 So, too, the frontals and parietals of Teleosts developed 

 independently of the cartilaginous skull, and belonged to 

 the skeletal system of the skin, not to the true vertebral 

 axial skeleton (pp. 215-6). Even more interesting was his 

 discovery, afterwards confirmed by Hertwig, 2 that in the 

 newt several .bones connected with the palate were formed 

 in the mucous membrane of the mouth by the fusion of a 

 number of little conical teeth (p. 97). Certain of these bones 

 he considered to be the substitutes, not the equivalents, of 

 the palatine and" pterygoid of other Vertebrates, which are 

 formed from the upper part of the first visceral arch, a part 

 missing in the newt (p. 100). Owing to the difference of 

 development he would not homologise these bones in the 

 newt with the palatine and pterygoid of other Vertebrates. 

 He recognised also that the bone now known as the 

 parasphenoid was developed in the frog in the mucous 

 membrane of the mouth, and had originally no connection 

 with the cranial basis (p. 34). Rathke in 1839 also allowed 

 the distinction between cartilage and membrane bone, but 

 laid no stress upon it (Entiv. d. Natter., p. 197). 



1 Vergl. Entwick. d. Kopfes d. nackten AmpJiibicn (p. 186). 

 - Arch.f. mikr. Anat., xi., Suppl., 1874. 



