ARCHETYPE OF SKULL 153 



they fuse. The side parts of the basisphenoid and pre- 

 sphenoid (forming the alisphenoids and the orbitosphenoids 

 respectively) develop in cartilage separately from the cranial 

 basis, not like the exoccipitals in continuity with it. The 

 hinder parts of the trabeculae become enclosed by two 

 processes of the basisphenoid ; their front parts remain in 

 a vestigial and cartilaginous state alongside the presphenoid. 

 The frontals and parietals show a peculiar mode of origin in 

 the adder, differing from their origin in other Vertebrates. 

 The frontals develop in continuity with the orbitosphenoids, 

 the parietals in continuity with the alisphenoids, and so have 

 much resemblance with the vertebral neural arches which 

 surround the spinal column (p. 195) 



Through Rathke's work the real embryonic archetype of 

 the vertebrate skull was for the first time disclosed. Rathke 

 discussed this archetype and its relation to the vertebral 

 theory of the skull in another paper of the same year (1839), 

 but before going on to this paper, we shall quote from 

 the paper on the adder the following passage, remarkable 

 for the clear way in which the idea of the embryological 

 archetype is expressed. " Whatever differences may appear 

 in the development of Vertebrates, there yet exists for the 

 different classes and orders a universally valid idea (plan, 

 schema, or type) ruling the first formation of their separate 

 parts. This idea must first be worked out, though possibly 

 with modifications, before more special ideas can find play. 

 The result of the latter process, however, is that what was 

 formed by the first idea is not so much hkiden as partially or 

 wholly destroyed" (p. 135). 



Rathke's general paper on the development of the skull 

 in Vertebrates l treats the matter on a broader comparative 

 basis than his paper on the adder, and takes into account all 

 the vertebrate classes, in so far as their development was 

 then known. He here makes the interesting suggestion, 

 later entirely confirmed, that the basis cranii or basilar plate 

 is first laid down as two strips, one on each side of the chorda 

 the structures now known as parachordals (pp. 6, 27). 

 For this supposition, he thinks, speaks the structure of the 



1 Bemerkungen iibcr die Entivickelung des Schadels der Wirbclthicre^ 

 Konigsberg, 1839. 



