Prof. H. G. Seeley on Hortalotarsus skirtopodus. 415 



The fibula is parallel to the tibia, and is exposed on its 

 external side. It is well preserved on the posterior aspect. 

 It shows no indication of close contact with the tibia at the 

 distal end. It appears to be slightly curved in length, being- 

 bowed outward, so that, although the extremities of the two 

 bones came near together, there is a fusiform interspace 

 between them which is eight or nine tenths of an inch wide 

 in the middle. About 1£ inch of the proximal end of the 

 fibula is lost. The fracture shows the bone to be compressed 

 from side to side, flat on the tibial side, convex externally, 

 js inch from front to back and \ inch from within outward. 

 As the bone extends distally it probably becomes subcylin- 

 drical in the middle, and then makes an oblique twist as it 

 widens to -^ of an inch at the distal end, where the antero- 

 external face is flattened, with the external margin inclined 

 backward, so that the end of the bone is somewhat oblique to 

 the tibia and its inner angle extends above the astragalus. 

 The posterior distal end of the fibula is more convex from 

 side to side. The transverse measurements over the distal 

 ends of tibia and fibula is 2^ inches, which is probably more 

 than the corresponding measurement over their proximal ends, 

 since both bones are compressed in form from side to side 

 proximally and expanded from side to side distally. 



The tarsus consists of two rows of bones (fig. 3). The distal 

 row is imperfectly preserved, but the proximal row consists of 

 astragalus, calcaneum, and a small intermedium. I am not 

 aware that the intermedium has previously been observed as 

 a separate ossification in any Saurischian, though Professor 

 E. S. Morse has identified the ascending process of the astra- 

 galus with that bone in both Ornithischia and Aves *. 



The astragalus is a transversely oblong bone which fits on 

 to the distal end of the tibia, and closely corresponds to it in 

 form, except that it is wider, extending a little beyond its 

 external margin. Its transverse measurement is l T 7 j inch j 

 it is \ inch deep in front, but posteriorly the depth is very 

 small, though it thickens a little towards the internal side. 

 The inner side has an antero-posterior measurement of /j 

 inch ; the external border is about two thirds as wide. The 

 anterior margin is slightly concave, the posterior margin 

 slightly convex, and the short sides incline a little backward. 



The articular surface is convexly rounded from front to 



* E. S. Morse, " On the Identity of the Ascending Process of the 

 Astragalus in Birds with the Intermedium," Anniversary Memoirs of the 

 Boston Society of Natural History, 1880. In that memoir the inter- 

 medium is found and figured in embryos of tern, petrel, sea-pigeon, 

 herring-gull, eider-duck, southern black-backed duck, penguin. 



