156 THE EMBRYOLOGICAL CRITERION 



(parietals), the presphenoid with its intercalaries (frontals), 

 and the ethmoid with its outgrowths (turbinals and cribri- 

 form plate), taking them in order from behind forwards, 

 show an increasing divergence from the plan according to 

 which vertebra; as commonly understood develop, so that the 

 basioccipital shows the greatest resemblance to a vertebra, 

 the ethmoid the least" (p. 30). 



In a posthumous volume published in 1861 the same 

 opinion is put forward. " In the head, too," he writes, " some 

 vertebra; can be recognised, although in a more or less 

 modified form. Yet at most only four cranial vertebra.- can 

 be assumed, and these differ from ordinary well-developed 

 vertebra: in their manner of formation the more the farther 

 forward they lie." l 



Rathke was an able and careful critic of the vertebral 

 theory of the skull, but he accepted it in the main. Actual 

 attack on the theory upon embryological grounds was 

 begun by C. Vogt, in his work on the development of 

 Coregonus? and in his paper on the development of Alytcs"* 

 He described for Coregonus an origin of the skull in the 

 main similar to that established by Rathke for the adder. 

 There was a "nuchal plate" in which the front end of the 

 notochord was imbedded ; the notochord ended at the level 

 of the labyrinth; there were two lateral bands, comparable 

 to Rathke's lateral trabeculre ; a " facial plate " was also 

 formed, which seems on the whole equivalent to the plate 

 formed by the fused anterior ends of the trabeculaj. A 

 little later the cranium formed a complete cartilaginous box 

 surrounding the brain, very similar to the adult cranium of 

 a shark. 



In his criticism of the vertebral theory of the skull, Vogt 

 started by defining the vertebra as a ring formed round the 

 chorda. Now since only the occipital segment of the skull 

 is formed actually round the notochord, the parts of the skull 



1 Enttvickelungsgeschickte der \\'irlh-ltlricre,\>. 142, 1861. 



-' /tnil>n't>lni;i<- des Sdlinoncs. A separate volume of L. Ayassiz's 

 Histoire nuturellc <lcs I'nissons d' Ran douce dc r Europe <-cn/r<i/c, 

 Neuchatel, 184?. 



' Untersuckungen fiber die Entwickelungsgeschichte der Gchiirtshel- 

 ferkri>(t, Solotluirn, 1842. 



