Annals of the Transvaal Museum 
275 
the figure, is not unlike that of Howesia, and quite manifestly the pelvis 
has been plate-like. 
The femur tibia and fibula call for no special remark. They are all long 
slender bones with little in the way of muscular impressions. The tibia 
measures 35-5 mm. 
The tarsus is fortunately perfectly preserved on the left side and part 
of the right one is also to be seen. It is the finest early Diapsid tarsus known, 
and one of the most important ever discovered. There is a large proximal 
element which I have elsewEere shown to be the intermedium and not the 
tibiale as generally believed, and a smaller proximal element, the fibulare, 
which forms a heel process. The intermedium has a very large articular 
surface for the tibia and a smaller articular surface for part of the fibula. 
The outer part of the intermedium is twisted somewhat forward so that 
when the tarsus is seen on the plantar surface this outer part is sunk in 
and looks at first like an additional element. There is a small foramen 
between the intermedium and the fibulare. The fibulare is a rounded flat 
bone only thickened where it articulates with the inner elements. It gives 
an articulation for part of the fibula. There is a fairly large tibiale which 
possibly gives a small articulation to part of the tibia when the foot is 
flexed. There are five distal tarsals. The first, second and third are relatively 
small, but the fourth is large and rather firmly articulated with the inter- 
medium and fibulare. There is a distinct and moderately large fifth tarsal 
which is closely articulated with the fibulare and the fourth tarsal. The 
metatarsals are all well developed and flattened rod-like bones. They 
increase in length from the first to the fourth. The fifth metatarsal is 
particularly interesting in that it shows no evidence of the peculiar hooking 
met with in the fifth metatarsals of Sphenodon, lizards and most allied 
forms of reptiles. In the specimen it is slightly imperfect but the proximal 
end is practically perfect and there is preserved the impressing of the distal 
end, so that the bone may be regarded as fully known. It is a little shorter 
than the first metatarsal and like it is only very slightly curved. The 
proximal end is much flattened and there is an outer process which was 
doubtless attached by a ligament to the fibulare. 
The striking points in the structure of Youngina are the remarkable 
skull, the sternum and the primitive tarsus and metatarsus. 
The skull is primitive enough to be ancestral to that of the lizards, 
Sphenodon, and all the later two arched types. The presence in it of a 
tabulare is particularly interesting. A tabulare is found in all the very 
primitive reptiles and is constantly retained in the mammal-like reptiles. 
In the phylum which gave rise to the two arched forms it becomes early 
lost. It is still retained in Ichthyosaurus and in the lizard-like Araeoscelis 
and in a few of the later two arched reptiles such as Sauranodon and 
probably Pleurosaurus , and in many lizards. Youngina shows us what is 
probably the ancestral condition in the two arched reptiles, and in the 
lizards which have been derived from them. 
The shoulder girdle is almost typically Sphenodon-like. But it is re- 
markable in retaining or possessing an ossified sternum. Ossified sterna 
are very rare in reptiles, but cartilaginous sterna are almost always present. 
The two flat sternal plates are strikingly like the sternal plates found in 
many Dinosaurs, and the ossifications in the sternum of Struthious birds. 
