the <SA:<J/ 0/ Diadeinodon. .'UO 



nu'diaii ai.d lateral areas of the oeeipnt^ and arc i'urtlier 

 remarkable lor the j)os.sessiou of large backwardly directed 

 |ilates similar to tiiose of Dicranozi/i/uiiia Icptuncelus, altliough 

 ai»iaiently imicli less developed. 



The oeeurreiice of a definite, loiip:, narrow, iuterpterygoid 

 vacuity was correctly described by Seeley. 



The fragments of lower jaw preserved seem to show that 

 the surangular was long and the coronoid j^J'Ocess very low. 



Some (jeneral considerations concerning the Structure of the 

 Cynodont Skull. 



The identifications of the bones which I have described 

 above depend on a comparison of the Cynodont skull with 

 tliose of other early and primitive reptiles. AH the deter- 

 minations are of old standings having mostly been made by 

 Ov\en or Seeley. 



1 follow liroom^s determination of the vomer as corre- 

 sponding to that of a mammal and being probably a modifi- 

 cation of the reptilian parasphenoid associated with the 

 development of a secondary palate. It is worthy of note 

 that in the crocodilian genus Metriorhynchus there is a 

 median vomer (Leeds, 1908) which is probably also a para- 

 sphenoid. 



The pterygoid is easily recognized, and comparison with 

 other early reptiles with the primitive reptilian (Rhyncho- 

 eephalian) palate shows that its remarkably slender posteiior 

 ramus and somewhat unusual articulation with the basi- 

 sphenoiil are to be correlated with the great reduction of the 

 quadrate and of all the bones which lie below the base of the 

 brain. Theromns })rovides an intermediate condition. 



The transverse hone has its usual relations despite its 

 considerable reduction. 



The identification of the various foramina depends on a 

 comparison with Sphenodon and a turtle, the broad columella 

 cranii of the latter rendering it rather more similar to a 

 Cynodont in the structure of the anterior part of the brain- 

 case. Starting at the back mc find that : — 



I. Nerve XII. issued by the notch on the rim of the 

 foramen magnum. 



II. Nerves XI., X., IX. issued through the la/ge pit 

 which exactly corresponds in its general relations with 

 the foramen jugulare of Sphenodon, 



