1878.J Mr. Parker on the Skull of the Common Snake. 13 



III. " On the Structure and Development of the Skull hi the 

 Common Snake (Tropidonotus natrix). By W. K. PARKER, 

 F.R.S. Received October 15, 1877. 



(Abstract.) 



For several years past I have taken every opportunity to work at the 

 skull of the common snake, bnt sufficient materials for completing a 

 memoir npon it have not turned np until lately. 



Last year, however, at the request of my friend Mr. P. H. Carpenter, 

 Dr. Max Braun, of Wiirzburg, kindly sent me about fifty early embryos 

 of reptiles ; these were of four kinds, namely, of the common snake, 

 the blind worm, the nimble lizard, and the gecko. 



These invaluable embryos, added to what I have for many years been 

 collecting, will enable me to bring before the Society a yearly tribute 

 of a paper on the skull of these instructive types. 



Lying at the very base of the gill -less Vertebrata, and possessing a 

 skull at once the simplest, and yet the most curiously specialized, the 

 snake is a type well worth careful study. I have found it so in my 

 own division of work. 



My guide in this piece of work has been Rathke, whose observations 

 on the early stages of the skull appeared first, in translation, in this 

 country, in Professor Huxley's " Croonian Lecture." 



For many years past I have known that the key to the meaning of 

 the skull in the whole series of the " Sauropsida " — reptiles and birds 

 in one huge group — was to be found in that of the serpent. I have 

 freely used it as such, and my nomenclature of the parrs of the grow- 

 ing bird's skull is based on that of the snake's, although, until now, I 

 have not been able to publish more than a mere abstract upon its 

 characters. 



For convenience' sake, I have divided my subject into seven stages. 

 the first of these being illustrated by embryos with a very delicate 

 vesicular head, bent down upon the neck, and whose entire length, 

 supposing them to be uncoiled, was barely three-quarters of an inch in 

 length. The last stage is the adult, whose skull, once interpreted, 

 will greatly help in the interpretation of all the skulls that rise above 

 and around it. 



As to the finished skull, it is easy to judge beforehand that the 

 cranial part must be a very solid and relatively small box, and that the 

 facial part must be free and elastic to the utmost degree. 



All the morphological specializations that take place in the head of 

 the embryo steadily lead to this result ; but the superstructure is mar- 

 vellously unlike the foundations that were at first laid. 



As to the general embryological study of the snake's embryo, it 

 may be remarked that it is almost exactly like that of the bird's. 



