282 ROBERT J. TERRY 



Orbito-temporal region 370 



Hypophyseal cartilage 370 



Fenestra basicranialis posterior 371 



Crista transversa and dorsum sellae 371 



Foramen hypophyseos 374 



Ala temporalis 374 



Pterygoid 380 



Carotid foramen 381 



Ala orbitalis 384 



Ethmoidal region 385 



Region of the olfactory fenestra 385 



Floor of the nose and Jacobson's cartilage 387 



Tectum nasi 390 



Paranasal cartilage 391 



Lamina antorbitalis 394 



Summary 396 



Literature 401 



Explanation of figures 405 



Abbreviations. ; 406 



Figures 409 



INTRODUCTION 



Studies of the primordial cranium of mamcmals have in most 

 instances dealt with but a single stage, and offer, therefore, 

 almost no data, on developmental processes. Moreover, there 

 seems to be a tendency, unfortunately, to pursue the study after 

 this manner and so to continue limiting inquiry to the methods 

 of comparative, descriptive anatomy. This criticism cannot 

 be made of investigation of the crania of the ichthyopsida. It 

 has been rather the rule than the exception for research in this 

 group to include as complete a survey of developmental processes 

 as the technique of the time permitted; that is, the studies pro- 

 ceeded toward the solution of cranial problems by comparative 

 embryological methods. No doubt, certain physical conditions 

 have in the one case been an obstacle to embryological work. 

 The difficulty of securing material in control and of sufficient 

 amount, and the great extent to which the investigation of even 

 a few stages leads one, are factors which have determined in 

 no small degree the methods and results of research on the 

 crania of higher forms. However, these difficulties are not 

 serious and should not stand in the way of gaining for the mara- 



