596 
MR. W. K. PARKER ON THE STRUCTURE AND 
and to overlap the work of my talented and esteemed friend, Mr. F. M. Balfour, of 
Cambridge. 
As my work is only a branch growing out of “ General Embryology,” I am not 
responsible for more proper embryological work than is sufficient for me, so that I 
may be able to graft my work on to the grand stock below. 
To no fellow-worker am I more indebted than to him whose name I have just 
mentioned, but I am deeply indebted to others also. 
The works and papers that have bestead me the most this time are the following, 
namely :— 
Professor Huxley’s ‘ Elements,’ pp. 219-244 (1864), and his ‘ Manual of the Anatomy 
of the Vertebrated Animals,’ pp. 193-271 (1871). 
Foster and Balfour’s ‘Elements of Embryology,’ Part I. (Macmillan and Co., 
1874.) 
Mr. F. M. Balfour’s Monograph ‘ On the Development of the Elasmobranch 
Fishes,’ 8vo. (Macmillan and Co., 1878.) 
Dr. A. Milnes Marshall, “ On the Development of the Cranial Nerves in the 
Chick ” (‘Quarterly Journal of Microscopical Science,’ vol. xviii., New Series, plates 2 
and 3, pp. 1-31.) 
In referring to my own papers, I may remark that the last, namely, that on the 
“ Snake’s Skull” (Phil. Trans. 1878, Part II., Plates 27-33, pp. 385-417), is most vital 
to the present piece of enquiry. 
Yet that paper, by itself, would have been a very poor guide to me in this ; I have 
been glad to fetch my knowledge from afar—from Amphibia and Fishes below, and 
from Birds and Mammals above, the special “ subject ” in hand. 
A cursory view of my figure of the upper surface of the Lizard’s skull might beguile 
the observer into supposing that it belonged to a Ganoid Fish, or at any rate to a 
Labyrinthodon, for the outer cranial elements are but little modified from what is seen 
in those types. 
But if we dig through the outer crust of the skull we shall find specializations of 
the most remarkable kind, some of which culminate in the typical Lizard, whilst others 
are anticipations, in an arrested form, of what carries the skull to so high a meta- 
morphic pitch in the Bird. 
No greater error, however, could be made than to suppose such a form as the 
Nimble Lizard parental to any kind of Bird ; it is a culminating type itself, although 
not running up to so great a height as its feathered relations. 
Yet we see in this Lizard notable beginnings of metamorphic modifications of the 
cranial elements that are positively meaningless in the creature itself, and the use of 
which is only to be seen where metamorphosis has had full swing in the skull of a 
high-class Bird. 
Moreover, some things, such as the articulation of the pterygoid bones with the 
skull, take place with the same fine detail of delicate metamorphosis in this Lizard as 
