1878.] Development of the Skull in the Lacertilia. 217 



of all such as gradually improved into the larval condition (for a long 

 while permanent) of the modern Batrachia, but they were Ametabolouh, 

 or arrested. 



These ancient bull-heads had a huge pharynx, under which, more 

 than behind, a very short abdomen was swung, with a snake-coiled 

 intestine ; their body was a mere lash, like the lash on the tail of the 

 larva of the smooth newt and Dactylethra, and the lash of the tail of 

 the adult Ghimcera. 



The forms from which the Marsipobranchii on the one hand, and 

 the Ghimcera on the other, sprung, were intermediate between the two 

 extreme forms imagined ; they were, however, close akin to the 

 primordial tadpole. 



What the pituitary body was, at that time, when the meso- 

 cephalic flexure just appeared ; how the vesiculation of the neural 

 axis arose ; and whether the sense- capsules were at first paired or 

 unpaired; of these things I will speak when I have obtained more 

 light upon this dark subject. 



But, even in the foggy illumination of the present, we can make 

 out that even the term " the vertebral theory of the skull," is absurd ; 

 vertebrae, as such, are a late specialization of a segmented creature, 

 whose mouth is opposite its nervous axis, and on the same aspect as 

 its main circulating organ (hsemostomous) . 



For a long while there was no definite division into head and 

 body; the Selachians show this to this day; their investing mass 

 or parachordal tracts run on from the head into the body without 

 division : the occipito-atlantal articulation is very late in its 

 appearance. 



Moreover, both the lamprey and Heptanchus show (or indicate) 

 that the head of modern Vertebrates has been greatly shortened — 

 much more than their throat ; the cervical vertebras are new segments 

 of the axis, intercalated at that part, to bind the shortening head to 

 the retreating body. 



This view is curiously strengthened by an observation of Mr. 

 Balfour's, with regard to the formation of " somatomes " in the 

 cervical region of the chick; the foremost do not appear first, but the 4th, 

 5th, 6th, &c, are to be seen first, and then the three front segments. 



Dr. Milnes Marshall's observations on the segmental nerves of the 

 chick,* showing that the third, or motor oculi, is as good a segmental 

 nerve as the great 5th, or trigeminal, and that the olfactory or first 

 nerve is developed exactly in the same manner as the other cranial 

 nerves, namely, from the dorsal region of the " epiblast ; " these 

 discoveries, I think, are of the greatest importance, and are very 

 suggestive. 



* See "Quarterly Journal of Microscopical Science," vol. xviii, New Series, 

 Plates 2, 3, pp. 1—31. 



