On Some Points in the Structure of the Dicynodont Skull. 347 



unlikely that one should be found in Anoniodonts. The study of the 

 Pelycosaurs showed that the American mammal-like reptiles are allied 

 to the South African, though in general structure rather more primi- 

 tive, but there is certainly a quadrato-jugal in the Pelycosaurs. We 

 now know that in the South African Dinocephalians Delpliinognatlius, 

 Tapinoceplialm, and Mosclwps there is also a well-developed quad- 

 rato-jugal. Eecently I have discovered that a quadrato-jugal is 

 present in Endothiodon, and as Endothiodon is a near ally of 

 Dicynodon, though rather more primitive, the discovery has com- 

 pelled me to still more carefully examine the condition in Dicynodon 

 and Oudenodon, and the skull of Oudenodon kolbei gives the oppor- 

 tunity desired. 



In Endothiodon the large plate which rests on the squarnosal is 

 evidently all quadrato-jugal, and the present skull proves that in the 

 Dicynodonts this large plate is also quadrato-jugal. The difficulties 

 have arisen from the fact that about the outer third of the articular 

 end, and which has always been regarded as quadrate, now proves 

 to be quadrato-jugal. The articular surface is of irregular quad- 

 rangular shape, of which the outer two-thirds are slightly convex 

 and the inner third has an antero-posterior ridge. Though all this 

 surface looks as if it were one bone, the quadrate, it is found that a 

 delicate suture runs across the outer convex portion in an antero- 

 posterior direction, dividing the surface into two. The outer portion, 

 which is little less than half, is quadrato-jugal, the inner is quadrate. 



The quadrato-jugal bone thus consists of an articular end and a 

 large flat plate affixed to the anterior side of the squarnosal. There 

 is probably a passage between the quadrate and the quadrato-jugal, 

 as in most reptiles. 



In connection with this discovery it is interesting to note that 

 Dr. Goodrich came to the correct conclusion a good many years 

 ago, as appears from a letter he sent me in 1903, in which he says : 

 " I was much interested to hear that you had succeeded in working 

 out the jaw articulation in Theriodonts, but I am still uneasy about 

 the identification of the bones of this region in the Dicynodonts. 

 Some time ago I made some notes in the British Museum, and 

 concluded that on the outer and anterior face of the squamosal 

 there is a bone with an upper squamous blade spreading over the 

 squamosal and a lower portion sharing to a small extent in the 

 formation of the articulation for the lower jaw. This bone is, I 

 believe, the one you call quadrate. But since it has more the 

 appearance of a membrane bone is apparently on the outer surface 

 alone and does not come into relation with the bones of the auditory 



