422 DR. 11. BROOM ON THE 



little more like the condition in mammals, the resemblance could 

 not have been very close. 



The stapes has long been an element which gave rise to 

 difficulties. So far as I am aware, the first author who gave a 

 good figure of the bone was P. Fischer, in 1870, and he regarded 

 the element as the pterygoid. From nearly all the British Museum 

 skulls it has been removed during development, but it still remains 

 and is well shown in the skull which forms the type of Kiste- 

 cephcdus chelydroides. Unfortunately, unlike most of Griesbach's 

 work, his figure of this skull in Owen's Catalogue is rather poor, 

 and in the description Owen says nothing about the bone in 

 question. But in any case, as Owen mistakes a portion of the 

 squamosal for the quadrate (his "tympanic''), though the quadrate 

 itself is present in a fairly well-preserved condition, it is manifest 

 that he had not a very clear idea of the structure of this part 

 of the skull, Seeley, when studying the Anomodont skull in 

 1888, took the massive stapes to be a malleus, and the unquestion- 

 ably homologous bone in the Cynodonts he later described as 

 possibly a " straight cochlea." Hitherto, I have always looked 

 upon it as the tympanic. Now we know that it is certainly the 

 stapes, though so very unlike the stapes of any living form. 



Though a considerable number of Anomodonts are known 

 showing the stapes in position and in perfect condition, I shall 

 describe and figure it and the related bones from the beautiful 

 specimen which I have recently made the type of Oudenodon 

 kolbei (PI. LVL figs. 4-6). The stapes is here a short dumbbell- 

 shaped bone with the ends flattened and slightly oblique. Across 

 one diagonal it measures 30 mm., across the other 23 mm. The 

 narrowest part of the middle measures 12 mm. across. When 

 viewed from behind the stapes is seen to be much flattened, the 

 narrowest part of the bone measui'ing only 4 mm. in thickness. 

 A considerable part of the inner end has probably been carti- 

 laginous. The outer end is much flattened and is closely articu- 

 lated to the inner side of the quadrate. There seems to be no 

 supra- or extra-columella, or if there has been one it must have 

 been relatively very small. 



The cjuadrate, one would readily think, would be the most easy 

 bone in the skull to identify. Many years ago Owen figured what 

 he believed to be the quadrate, and nearly everyone has agreed 

 with his determination. There is a large articulation, about as 

 broad as long. Along its inner third there runs an antero- 

 posterior ridge ; near the middle there is an antero-posterior 

 shallow groove ; and the outer part of the articulation is a convex 

 disc. This outer part forms the base of a bone which on passing 

 upwards becomes a Avide fan-like squamous plate, which is closely 

 applied to the squamosal. If the whole articulation be quadrate 

 thjs squamous plate must also be quadrate, as has been the view 

 of Owen, Seeley, and myself. It would now appear that about 

 half of the articulation is formed by the quadrato-jugaJ, and that 

 the s(|uamous plate is also thus quadrato-jugal. 



The squamosal comes down behind the quadi'ate and quadrato- 



