1904.] OF THE THERIODOXT MAKDIBLE. 491 



part of the squamosal. The whole of the mandibular articulation 

 is formed b}^ the articular bone. The exact size of the bone is 

 not seen in the specimen as it is largely ovei'lapped by the 

 angular. 



The angular is seen between the posterior and under border of 

 the dentary and the articular bone. As seen in the specimen, it 

 appears to be a thin flake of bone lying on the outer side of the 

 articular. A good deal of the bone has, however, been removed 

 while the specimen was being developed, and the angular should 

 extend as far back as the groove which is seen on the outer side 

 of the postei'ior part of the left jaw. 



The surangular is not very well seen in this specimen. 



The splenial, except on the fractured surface at the front of the' 

 specimen, is also imperfectly displayed. 



The quadrate is well shown on the left side and fairly well on 

 the right. In the development of the specimen this region has been 

 to some extent gi^ound down, but this has resulted in the rela- 

 tions of the quadrate to the articular and to the squamosal being 

 well shown. In fig. 1 (PI. XXXV.) the quadrate is seen inter- 

 digitating with the sqiiamosal, almost exactly as in Cynognathus 

 C7-ateronotus. On the outer side of the articulation, the articular 

 comes almost in contact with the squamosal, and it seems not 

 improbable that the articulation of the mandible is here directly 

 with the squamosal. On the right side, only a part of the middle 

 and of the inner end of the quadrate is seen. 



Passing directly inwards from the inner end of the quadrate 

 there is seen on both sides a very remarkable elongated bone. As 

 it is now seen in the specimen, it appears to be a somewhat 

 cylindrical bone, hollow in the centre, and from which part of the 

 thin wall has been removed during the removal of the matrix.. 

 Its outer end evidently articulates with the quadrate, and the 

 inner end with a part of what may be the peiiotic. Seeley 

 recognises that this bone is evidently the homologue of the dumb^ 

 bell-like bone in the similar situation in Dicynodon — the bone: 

 which, when dealing with the Anomodonts, he believed to be the 

 malleus. In his paper on Cynognathtis (1895) he says: " I now. 

 incline to regard it as a rudimentary straight cochlea." In 

 describing the skull of Udenodon in 1901 (2), I expressed the 

 opinion that the bone in the Dicjiiodonts was the homologue of 

 the mammalian tympanic, and I still incline to this opinion. In 

 Udenodon the bone is solid, so that it cannot have lodged any 

 part of the inner ear. In Dicynodon the columella auris lies in 

 the hoUow formed by the bone and the exoccipital. In Cyno-. 

 gnathus there is likewise a hollow between the exoccipital (" opisth ■ 

 otic " of Seeley) and this supposed tympanic, and in this hollow 

 there lie one or two tiny bones or portions of bones which may 

 represent the auditory ossicles. 



Two other specimens probably of one individual, and belonging 

 to a species of Cynognathus (either C. herryi or a new species), 



