66 Prof. Owen on the Reptilian Fossils of South Africa. 



(fig. 2, /) is pierced just within the brim of the orbit, and defended by a protu- 

 berance of the lachrymal bone in front of it. 



The bony anterior apertures of the nasal cavity (n) are separated above by a 

 space two-thirds of an inch in breadth, and formed principally by the nasal bones, 

 between the anterior ends of which, the median ascending process of the inter- 

 maxillary bone is wedged. The shape of the nasal openings (w) is a longitudinal 

 ellipse ; they are situated about half an inch in advance of the orbits, are defined 

 above by a sharp overhanging border of the nasal bones, and the lower boundary, 

 which is formed by the superior maxillaries (20) , is rounded off into the nasal 

 cavity : the plane of the opening being much nearer the perpendicular than is that 

 of the orbit. In the Crocodiles the plane of the single median bony nostril is 

 horizontal ; in the Chelonia it is nearly or quite vertical ; in the Lizards the nostrils 

 are double ; and in many, as Uromastyx and Rhynchocephalus, are as lateral in po- 

 sition and aspect as in the Dicynodon. A very remarkable feature of the present 

 fossil cranium is the swelling out of the superior maxillary and malar bones below 

 the orbits, which part is the point d'appui of four strong bony columns : one of 

 these is formed by the lachrymal (16) and pre-frontal (14) and descends in front of 

 the orbit ; a second, formed by the malar (20 a) and post-frontal Cll)j descends be- 

 hind the orbit ; the third, formed by the zygomatic (27), extends longitudinally from 

 the back part of the malo-maxillary protuberance to the tympanic pedicle ; the fourth, 

 contributed by the 'os transversum,' is continued from the under part of the maxillary 

 bone, anterior to the orbit, downwards, backwards and inwards to abut against the 

 pterygoids. The superior maxillary bone commences anteriorly by a suture, very 

 distinctly shown in a specimen of the fore-part of the cranium of the Dicynodon 

 testudiceps*, which extends down from the nostril to the alveolar border of the 

 upper jaw ; the bone extends backwards, forming the lower border of the nostril, 

 and uniting with the lachrymal bone, as it passes to the lower part of the orbit ; 

 then expanding rapidly, as it proceeds, to coalesce with the malar bone. This ex- 

 panded suborbital part of the maxillary bone or malo-maxillary bone, supported 

 by the four converging stout osseous columns above described, is excavated by a 

 wide and deep conical alveolus, with a circular area of equal diameter, — half an 

 inch, — to its closed base, and lodging a long and strong, slightly curved and sharp- 

 pointed canine tooth or tusk, which projects about two inches from the open 

 extremity of the produced socket. The direction of the tusks is forwards, down- 

 wards and very slightly inwards ; the two converging, as they descend along the 

 outer side of the compressed symphysis of the lower jaw. The fractured state of 

 the fore-part of the present fossil cranium anterior to the nostrils prevents the 



* PI. VI. fig. 1. 



