STRUCTURE OF THE REPTILIAN TARSUS. 



149 



and it is remarkable, as I hope to show presently, that a similar 

 shifting of tlie tibiale is also seen in Sauropsida, and perhaps 

 it has arisen independently in this group. 



In Gasea hroilii Williston (text-fig. 9) the small central element 

 has disappeared, and we thus have a tarsus that, except for 

 retaining the fifth tarsale, is essentially mammalian in structure. 



In Varanops hrevirostris (Williston) (text- fig. 10) the tarsus is 

 like tliat of Casea and Ojihiacodon, except that not only has the 

 centrale disappeared, but the tibiale is evidently cartilaginous. 



In the Therapsids the tarsus is almost typically mammalian 

 in structure. _ 'lliere is never a centrale, and the tibiale is always 

 placed, as is the navicular in the mammal, between the inter- 

 medium and the first and second tarsals. 



In Anomodonts the tibiale is frequently cartilaginous either 

 wholly or in part. Many years ago I figured the tarsus in a. 

 small form which I referred to Udenodon gracilis Broom. Shortly 

 afterwards I found that the skeleton belonged to the same animal 



Text-fioure 10. 



Text-figure 11. 



Text-fieure 12. 



Text-fig. 10. — Right tarsus and metatarsus of Varanopfs bremrosMs (Williston). 

 A primitive Pt'lycosauroid reptile. After Williston. 



Text-fig. 11. — Rig-lit tarsus and metatarsus oi Mni/dopsis trigoniceps (Broom), a small 

 Anomodout reptile. The drawing is mainly from the specimen in the Alljany 

 Museum, but partly restored from other specimens. The condition of the 

 tibiale varies greatly in Anomodonts. In some it is completely cartilaginous, 

 in others well ossified. It probably affords part of the articulation for the 

 tibia. 



Text-fig. 12. — Right tarsus and metatarsus of Galechirns sclioltzi Broom, a small 

 Dromasaurian reptile. The elements are figured as found, but the inter- 

 medium is evidentlj^ slightly rotated. 



as the skull which I had called Oudenodon trigo?iiceps Broom. 

 We now knoAv that this small Anomodout has a few small molars, 

 and must be placed in a new genus, Einydojjsis. I give a new figure 

 of the tarsus (text-fig. 11). The interesting point about it is 

 that the tibia probably articulates with the tibiale. In another 

 small Anomodout tarsus I have belonging to an undescribed 

 species, the tibia also appeared to articulate with the tibiale. 



In the more mammal-like forms — the Gorgonopsians and the 

 Cynodonts — the tibia and fibula articulate only with the inter- 

 medium and the fibulare. 



