DEVELOPMENT OF THE SKULL OF EMYS 695 



plate method of an embryo of Emys lutaria in which the carapace 

 measured 11 mm. in length. The model represents the cartilagi- 

 nous skull magnified fifty times with the membrane bones of the 

 left side removed. At this stage the cartilage is well developed 

 and ossification has not proceeded far enough to alter materially 

 the original form of the chondrocranium. The membrane bones are 

 fairly well developed although the parasphenoideum and quad- 

 ratojugale as well as the complementary of the lower jaw appear*^ 

 first in older embryos than that modelled. The present study 

 undertakes to determine the course of development of the chelo- 

 nian skull from its early prechondral stage. A series of embryos 

 and young with carapace lengths ranging from 4.7 mm. to 28 

 mm. forms the basis of the work. 



It gives me pleasure to make the following acknowledgments: 

 to Herr Professor Gaupp for the suggestion of the problem in the 

 first place as well as for his constant valuable criticism and sug- 

 gestions, and for the generous loan of many series of sections of 

 Lacerta and Chelone embryos and of many papers from his pri- 

 vate library; to Herr Professor Keibel who furnished me with a 

 large number of embryos of Emys lutaria which were collected by 

 JVIehnert ; and to Herr Geheime Rat Wiedersheim for the courtesies 

 and facilities of the Anatomisches Institut of Freiburg i. B. 

 where most of the work was done during the college year of 1910- 

 1 1 . To my father I am under obhgation for material aid without 

 which the present investigation could hardly have been under- 

 taken. 



GENERAL FORM OF THE SKULL 



The cartilaginous skull of Emys lutaria resembles rather closely 

 in its essential features that of Lacerta which has been so fully 

 described by means of models by Gaupp ('00). The Chelonian 

 skull is less elongated than that of Lacerta, especially in the ante- 

 rior half, as is shown by the relatively anterior position of the 

 fenestra hy]3ophyseos. This is due principally to the fact that the 

 septum interorbitale of the turtle is much shorter than in the 

 lizards and the olfactory capsule, as will be shown later, is bent 

 ventrally so that it comes to lie to a greater extent ventral rather 

 than anterior to the orbital portion of the skull. Besides being 



