Prof. Owen on the genus Dicynodon. 07 



recognition of its exact form and extent, and also the more important determina- 

 tion of the structure of the intermaxillary bone (19). This deficiency is, however, 

 amply compensated by the perfect state of the fore-part of the skull of the alUed 

 species, Dicynodon testudiceps ; in the description of which, the affinities deducible 

 from the modifications of the intermaxillary and palatal regions will be more fully 

 discussed. 



I may observe however, that in the present specimen of the Dicynodon lacer- 

 ticeps, the fore-part of the upper jaw has been longer and more compressed 

 than in the other recognizable species of the bidental genus, and that no trace 

 is perceptible of any other teeth than the two long canine tusks above de- 

 scribed. It is evident that the carcase of the old reptile to which the skull in 

 question belonged must have been buried in the sand, which subsequent consoli- 

 dation converted into the present hard matrix, soon after death, and there have 

 rested undisturbed until its discovery by Mr. Bain : for the lower jaw has not 

 suflfered the smallest dislocation from its natural junction with the extremities of 

 the tympanic pedicles ; and this is not a joint where there is close interlocking of 

 the opposed surfaces of the bones, as in the mandibular articulation of the Badger 

 and some other Mammalia. A shallow cavity, cut obliquely in the posterior part 

 of the lower jaw, receives the corresponding slight convexity at the end of the 

 tympanic pedicle. Thus attached, the lower jaw has been cemented by the sur- 

 rounding rock in its natural position, but with the mouth a little open. The skull 

 of the Rhynchosaurus* from the new red sandstone at Grinsill near Shrewsbury 

 has the lower jaw similarly preserved, showing the same speedy entombment and 

 subsequent undisturbed repose in that triassic matrix. 



The lower jaw manifests by its great depth as compared with its length, and by 

 its edentulous condition, a close and important relationship between the Dicynodon 

 and Rhynchosaurus ; but this part of our ancient African Lacertian deviated still 

 further from the ordinary proportions of the lower jaw in the Crocodiles and Lizards, 

 and more closely resembled that of the Tortoises and Turtles, in being still shorter 

 in proportion to its depth than in the Rhynchosaur : it appears, however, to have 

 differed from the lower jaws of all other known recent and extinct Reptiles, by the 

 evident traces of a strong longitudinal ridge projecting outwards from the middle 

 of the external surface of each ramus. A feeble rudiment of such ridge is present 

 in the lower jaw of the Rhynchocephalus figured, and is developed, as in the Dicyno- 

 don, from the dentary piece. There is no trace of teeth or their sockets in the lower 

 jaw of the Dicynodon testudiceps : so much of the alveolar border as is exposed pre- 

 sents a smooth and even edge, which seems to have played like a scissor-blade upon 

 the inner side of the corresponding edentulous border of the upper jaw ; and it is 



* Report of British Association, 1841, p. 145. 



