144 



DR. R. BROOM ON THE 



undisturbed positions. Still, we have a few early tarsi sufficently 

 well preserved to suggest to us the main lines of evolution. 



The most primitive Tetrapod tarsus known is that of the 

 Temnospondylous amphibian, Trematops viilleri Williston, from 

 the Lower Permian Beds of North America (text-fig. 1). Here we 

 find the tarsus composed of four large proximal elements, one 

 of which is situated centrally, five distal tarsalia and three centralia 

 lying above the first, second, and third tarsalia. The element 

 articulating with the end of the tibia we ought, I think, to call 

 the tibiale, even though it is not, as I hope to show, the same 

 element as articulates with the tibia in the higher forms. The 

 other two proximal elements must be regarded as the fibulare and 

 the intermedium. These determinations are those of Williston, 

 and it is difficult to see how they can be disputed. Williston 

 points out that there has been a passage for vessels between the 

 fibulare and the intermedium. 



Text-figure 1. 



Text-fig. 1. — Right tarsus and metatarsus of Trematops milleri Williston*, 

 slightly modified after Williston. 



Text-fig. 2. — Right tarsus and metatarsus of TJranoceutroclon senekalensis 

 v. Hoepen f. The tarsal elements are figured in true relative position, 

 as seen in two different specimens. Letters indicate the probable 

 position of the elements which have remained cartilaginous. 



* An American Lower Permian Temnospondylous Amphibian. 

 f A South-African Upper Permian Temnospondylous Amphibian. 



Our South African Upper Permian Temnospondylous form,. 

 Uranocentrodon senekalensis v. Hoepen . (text-fig. 2), gives us a 

 further development of the amphibian tarsus. Though the tarsus 

 is here imperfectly ossified, we have two specimens with the 

 elements in almost undisturbed relations, so that we can be fairly 

 sure of their determinations. As will be seen from the figure 

 I give, there are three large, proximal, well-ossified elements and 

 three imperfect ossified distal elements. If we had not the clue 

 afforded by Trematops, we might determine the proximal elements 

 as the fibulare, intermedium, and tibiale. We might perhaps, even 



