120 Bulletin American Museum of Natural History. [Yo]. XXVII, 



In nnimmals this lateral vibration of the posterior end of the jaw, M'hen the 

 clentary came into contact with the squamosal (see below) may have condi- 

 tioned the development of a transversely oval condyle. 



The skull of Galesaurus, a small ally of Cynognathus, is in top and side 

 view nnu'h like that of Didelphts, the resemblance extending even to the 

 nasals, which broaden posteriorly in a characteristically Marsupial fashion 

 (Owen, 1876, pi. xviii, fig. 8). The jugal has a strong postorbital process, 

 which is continuous with the postorbital process of the postorbital above. 

 In the Carnivorous ^Marsupials the malar also extends forward and sends 

 up a postorbital apophysis (Fig. LI, p.o.Ma.). 



The characters of the mammalian zygomatic arch are completely real- 

 ized in Bauria (Broom, 1909.1, }). 272), since in this Cynodont the jugal 

 (malar) is not connected with the post-orbital, so that the orbit remains 

 open posteriorly. 



The practical identity in the characters of the base of the skull ' in 

 Galesaurus, Cynognathus and Gomphognathus indicates the close ordinal 

 alliance of these genera to each other (of. Seeley, 1895.4, p. 139 and 

 1895.3, p. 24). This region (Fig. 1, B) seems to show certain underlying 

 resemblances to the genei'alized mammalian condition in so far as they are 

 preserved in the skulls of Didelphis and Thylacynus (Fig. 1, A). The hard 

 palate, though as yet confined to the anterior part of the skull, is composed 

 of the same elements as in the mammals. The apparent large size and 

 relations of the pterygoids at first sight a])pear as a very fundamental differ- 

 ence from the mammalian skull; but Broom has very recently determined 

 (1909.3) that the pterygoids, unlike those of typical reptiles, did not extend 

 back to the cjuadrate, but were comparalile, in their relations with the sur- 

 rounding bones, to the pterygoids of mammals. The remaining differences 

 between the pterygoids of Cynodonts and those of mammals may be ex- 

 plained as a result of three simultaneous processes: (1) the backward 

 prolongation of the palatines caused the posterior border of the latter bones 

 gradually to usurp the position of the anterior flanges of the pterygoids; (2) 

 the reduction of the articular {\^. 140) of the lower jaw caused the reduction 

 of the powerful pterygoid muscles which were inserted on the articular and 

 attached to the pterygoid flanges. (3) Perha])s in order to support the 

 pterygoid muscles the alisphenoids sent down a flange on either side, external 

 to the pterygoids, which were finally reduced to mere scales of bone. But in 

 spite of all these reductions the pterygoids in primitive mammals still retain 

 their ancient contact with the ]:)alatines and still extend inward below the 

 floor of the sphenoids (c/. Fig. LI, pt). 



1 As may be observed upon casts of the original skulls. 



