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



upwards and backwards from the side of the summit of the neural arch ; its free 

 portion or extremity is broken off. The spinous process [ns) inclines a little back- 

 wards, and is compressed with a sharp anterior border. 



The following are the dimensions of this vertebra : — 



In. Lines. 



Length of centrum 1 .5 



Breadth of centrum 2 



Height of centrum 1 10 



Length of spinous process 2 



Antero-posterior diameter of spinous process . . 10 



Total vertical diameter or height of the vertebra . 5 



Transverse diameter of neural canal 7 



This remarkable vertebra combines peculiarities borrowed, as it were, from 

 different genera of Saurians. In the proportions of the centrum, neural arch, and 

 spine, it resembles the vertebrae of the Plesiosaurus ; in the deep concavity of each 

 articular end, it resembles the vertebrae of the Ichthyosaurus, the Perennibranchiate 

 Batrachians, and Fishes. The indications of the twofold articulation of the thoracic 

 rib, viz. by a head to the centrum and by a tubercle to the transverse process, 

 mark an affinity to the Crocodiles and Dinosaurs, and make it probable that the 

 Dicynodon possessed the higher structure of the heart which characterizes the 

 Crocodilia among existing reptiles. 



Sacrum. — Of this characteristic part of the vertebral column there are two 

 exemplifications (PI. XXXIIL figs. 5 & 6), which are respectively either the entire 

 sacrum of two distinct species, or are parts of the same sacrum, or of the sacrum 

 of the same species. Each specimen consists of two vertebrae, anchylosed, and with 

 the usual unmistakeable sacral modifications of the articular surfaces of the centrums 

 and developments of the pleural elements. But these elements are so differently 

 modified in each, as clearly to determine a difference of one or the other of the two 

 kinds above mentioned. I shall first describe the sacrum, or portion of sacrum, 

 figured in PI. XXXIIL figs. 4 & 5, next that represented in figs. 6 & 7, and finally 

 give the grounds, from the comparison of the two, which incline me to the conclu- 

 sion that they are parts of the same sacrum according to the type of the Dinosauria, 

 rather than two different sacrums with the restricted number of vertebrae charac- 

 teristic of the recent and fossil Crocodilian and Lacertian reptiles. 



The specimen (PI. XXXIIL figs. 4 & 5) includes two vertebrae, the bodies of 

 which measure together five inches in length, and are three inches across the 

 expanded articular ends, which are nearly flat. The lower half of the anterior of 

 these vertebrae (fig. 5) has been broken away ; what remains of the anterior 

 expanded end is slightly concave. The head of the sacral rib {pi) is of very great 



