C 385 ] 
XII. On the Str ucture and Development of the Shull in the Common Snake 
(Tropidonotus natrix). 
By William Kitchen Parker, F.R.S. 
Received October 15, 1877, — Read January 10, 1878. 
[Plates 27-33.] 
The most important work on the development of this type appeared as long ago as 
1839. It was by the late Professor H. Bathke, ‘ Entwickelungsgeschichte der Natter 
( Coluber natrix).’ Konigsb., 4to. 
From time to time during the last twelve years I have worked at the Snake’s 
skull, my guide being Professor Huxley’s translation of so much of XvATHKe’s work 
as bears especially upon my line of research ; this I have had at hand, both in the 
‘ Croonian Lecture ’ and in the ‘ Elements of Comparative Anatomy.’ My earliest 
studies of the embryonic conditions of the Snake’s skull were made on half-grown 
embryos of the Python (Python S eh ce), and of the Anaconda (Eunectes murinus) ; these 
were the gift of my friends Dr. Edwards Crisp, F.Z.S., and Dr. P. L. Sclater, F.R.S. 
Meantime I have been acquiring younger and still younger specimens of the Common 
Snake, but only lately have I succeeded in obtaining any embryos sufficiently 
immature for my first and second stages. During the last winter (February, 1877) 
these earlier stages happily came to hand. At the instance of Mr. P. H. Carpenter, 
M. Braun, of Wurzburg, sent me a considerable number of reptilian embryos in 
very early stages, from Professor Semper’s laboratory. These included, besides the 
longed-for specimens of the Common Snake, others of the Blind Worm (Anguis fragilis ), 
the Nimble Lizard ( Lacerta agilis ), and the Gecko (Platydactylus). These other three 
types I intend to work out in due time. The Snake has the simplest skull of al] ; 
and yet, simple as it is, it is a key to that of any member of that great bundle of Ver- 
tebrate life which, including the reptiles and birds, is termed “ Sauropsida.” (See 
Huxley, “On the Classification of Birds,” Proc. Zool. Soc., April 11th, 1867, 
pp. 415-472.) 
Having wrought very much at the morphology of the Birds’ skull, the simple 
condition of the skull in such a type as the Snake — which lies down at the very base 
of the huge group of which the Bird forms the very top and crest — has been to me 
the most instructive ; many things in the utterly specialized avian skull would, but 
for this key, have been quite beyond my power of interpretation. 
In this stage of my work I am able to compare the early conditions of the Ophidian 
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