170 DB. R, BROOM ON THE STRUCTURE AKD [June 4, 



the thoracic series ; and in Udenodon, as in most other Thero- 

 morphous reptiles, there is no division of the body vertebrae into 

 thoracics and lumbars. Assuming that the first cervical vertebra 

 displayed is the 3rd cervical, then it is moderately certain that in 

 U. gracilis there are 27 presacral vertebrae. 



The vertebrae which I take to be 3rd and 4th cervicals, so far as 

 displayed, agree fairly closely with the 3rd and 4th cervicals of 

 Tropidostoma dunni Seeley (5) [ = according to Lydekker (7) 

 Ptychosiagum microtrema Seeley]. The bodies of the vertebrae 

 have well-marked lateral processes arising from the anterior and 

 outer angles of the ventral surfaces, for articulation with the 

 cervical ribs. 



In the skeleton of Udenodon gracilis, though most of the 

 vertebrae of the thoraco-lumbar series are shown, unfortunately 

 only the bodies are displayed ; but in the imperfect skeleton of 

 U. haini (spec. 4) a number of presacral vertebree are well 

 preserved. 



As has long been known in other Dicynodonts, the vertebrae 

 consist of deeply cupped bodies to which are articulated arches 

 closely resembling the arches in mammals. In the dorsal series 

 (c/. Plate XVII. fig. 4) the bodies are considerably elongated 

 and moderately constricted in the middle. On the body just 

 below the neuro- central suture in front is the articular surface 

 for the head of the rib. The pedicle is stout, and a ridge runs up 

 obliquely from near the front of the neuro-central suture to the 

 transverse process. The transverse processes {tr.) are short and 

 strong, directed outwards and slightly upwards, and lie well above 

 the level of the top of the neural canal. The spine {sp.) is quite 

 short, and situated well backwards over the posterior zygapo- 

 physes. Both the anterior and posterior zygapophyses are 

 situated fairly closely together, and the articular surfaces make 

 approximately a right angle with each other. A large opening is 

 formed between each pair of vertebrae for the exit of the spinal 

 nerves. 



The ribs in the thoracic region (c/. Plate XVI.) are long and 

 slender ; the anterior ones being, however, slightly stouter than the 

 others. The upper end of the rib is expanded so as to form a 

 distinct head for articulation with the centrum and a tubercle for 

 attachment to the transverse process. As the border of the rib 

 between the head and the tubercle is almost straight, and the 

 ridge on the vertebra between the articular surface and the 

 transverse process is only slightly concave, there must be but 

 little of a foramen left between the rib and the vertebra. The 

 ribs in the lumbar region have their upper ends less expanded 

 and may possibly have been articulated to the transverse processes 

 alone. 



The sacrum is very badly preserved in the skeleton of U. gracilis, 

 but appears to have been composed of 5 vertebrae. 



The tail has evidently been short, but it is impossible to say 

 of how many vertebrae it may have been composed. Those that 



