168 DK. B. BBOOM OTST THE STEUCTUBE AND [June 4, 



antero-posterior groove running across it, which divides it into 

 an outer semicircular button-like portion and an inner very 

 prominent antero-posterior ridge. Both the outer and inner 

 portions of the articular face have an antero-posterior convexity 

 o£ fairly wide radius. 



The structure of the palate I have elsewhere dealt with (6), 

 and I have little further so add to my previous description. The 

 pterygoids, as in the other Dicynodonts, are greatly developed, 

 meeting each other in the middle line and sending processes 

 forwards to the maxillse and backwards to the quadrates. Between 

 the two anterior processes lie the palatines and the vomer. The 

 vomer is quite mammalian in structure, and is present as a 

 median plate, extending from the fork formed by the anterior 

 branches of the pterygoids forwards to articulate with the palatal 

 median and internal median ridges of the premaxilla. Superiorly 

 the vomer articulates with the sphenoid, the mesethmoid, and 

 the ethmoid cartilage. Towards the posterior and upper part 

 it gives off: a pair of small lateral wings which articulate with 

 the palatines, and Avith them form the roofs of the nasal passages. 

 The palatines pass outwards and downwards from the articu- 

 lations with the vomer, by the side of the anterior branches of the 

 pterygoids. Each palatine then sends a process forwards and 

 inwards to form a sort of rudimentary secondary palate, and a 

 second process outwards above the anterior lobe of the pterygoid 

 to meet the jugal. 



Where the two pterygoids meet in the middle hue they rest on, 

 and are articulated to, the basisphenoid. This latter bone shows 

 on the under surface of the skull to a considerable extent, sending 

 two plates backwards to clasp the large paroccipital. processes. 

 From the region where the pterygoids meet, the basisphenoid sends 

 a comparatively narrow median plate upwards and forwards 

 resting on the vomer, and probably in adult specimens articulating 

 with the mesethmoid. This plate may be the presphenoid, but I 

 have not seen any specimens in which it is distinct from the basi- 

 sphenoid. The mesethmoid is a median plate which forms the 

 greater part of the interorbital septum. Above it is clasped by 

 the orbital plates of the frontals, and below it rests on the 

 vomer. 



Immediately behind the point where the pterygoids meet, there 

 passes upwards from each pterygoid a slender columella cranii. 

 In forms with a deep narrow skull, e. g. U. greyi, the columella is long 

 and slender : in those species where the skull is broad and rather 

 flat, the columella is comparatively short. In all forms, however, 

 it is very slender. It appears to articulate with the parietal above. 



The peri otic bones appear to form the lateral walls of the brain- 

 case in a manner very similar to that seen in lizards ; but I have 

 not seen any specimens in which their exact limits could with 

 certainty be determined. 



The occiput has long been well known in a number of Dicy- 

 nodonts, especially Ptychosiagum. A small occiput is figured by 



