STRUCTURE OF THE REPTILIAN TARSUS. 



149 



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

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

 it has arisen independently in this group. 



In Casea broilii 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 brevirostris (Williston) (text-fig. 10) the tarsus is 

 like that of Casea and Ophiacodon, 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. There 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-fi«ure 10. 



Text-figure 1 1 . Text-figure 1 2 . 



13^ 



I3lr 



Text-fig- 10. — Rig-lit tarsus and metatarsus of Varanops brevirostris (Williston). 

 A primitive Pelycosauroid reptile. After Williston. 



Text-fig. 11. — Right tarsus and metatarsus of Emydopsis trigoniceps (Broom), a siiiiill 

 Anomodont reptile. The drawing is mainly from the specimen in the Albany 

 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 Galechirus sclwltzi Broom, a small 

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

 medium is evidently sliglithy rotated. 



as the skull which I had called Oudenodon trigoniceps Broom. 

 We now know that this small Anomodont has a few small molars, 

 and must be placed in a new genus, Emydopsis. 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 Anomodont 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 

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

 medium and the fibulare. 



