900 DR. R. BROOM OX THE 



jugal a rather feeble postorbital arch. The zygomatic arch is 

 formed by the jugal and the squamosaL The jugal extends 

 nearly back to the articular region, and the squamosal n.early 

 forward to the base of the postorbital arclK The squamosal is 

 not unlike that of Bauria, but the zygomatic portion is much 

 better developed ; so that as regards the squamosal Nythosaurtts 

 is intermediate between Baurki and Cynognathus. The quadrate 

 is of the same type as in the better known Cynognathus. 



The palate, so far as known, agrees fairly well with the Cyno- 

 gnathus type, and the occipital condyle is double.. 



The lower jaw has a large dentary, but there is no trace even 

 of a condylar process. The angular and surangular are fairly 

 large and still resemble considerably the Therocephalian type. 

 The articular also resembles that of the earlier rather than that 

 of the later types. 



Nythosauru-s is perhaps the most mammal -like of the known 

 Cynodonts. The zygomatic arch is exceedingly like that of most 

 primitive mammals, and if the prefrontal and postorbital bones 

 were lost and the internasal process of the premaxilla aborted 

 there would be nothing left in the side view of the skull to 

 distinguish it from that of a mammal. The lower jaw with its 

 fairly large angular and surangular is still much less like the 

 mammalian condition than what we see in the higher Cynodonts, 

 and the articular is of the same primitive type seen in Bauria. 



The dentition though very pi'imitive is considerably more 

 highly evolved than in Bauria.. The formula, i. ^, c. -^, m. ^, 

 comes very near to that of the typical mammal, and that of 

 Galesaurus, L ^, c. i, m. j|, is near that of the ancestral mammal. 

 The difference in the teeth in some of the specimens of Nytho- 

 smw^s is apparently due to the fact that in some the teeth belong- 

 to the first set and in others to the second. 



CynognaiJiihs^ 

 (PL XLVL figs. 1 cfe 2, and text-figs. 171, 172.) 



The genus Cynognathios is known by the very fine skull of 

 C cratermwtus in the British Museum, the type skull of C.jilaty- 

 cejys in the Albany Museum, a fairly good skull of C. herryiin the 

 S. African Museum, and three or four less satisfactory specimens. 



Seeley has given a fairly full account of the skiill of Cyno- 

 gnathus crateronotus, but unfortunately a number of his figures are 

 so indifferently reproduced that they convey no more to the 

 student than does the plaster cast. And further, while most of 

 his determinations are correct, he unfortunately suggests so many 

 alternative possibilities that the moi'phologist is left compara- 

 tively helpless. 



The figure given by Seeley of the side view of the skull of 

 C. crateronotus gives an excellent idea of the general form of the 

 skull and of the structure of the teiTiporal region, except that the 



