Annals of the Transvaal Museum 
131 
The articular is broad behind. It apparently fits into a hollow of the 
quadrate. Nothing can be said of the articulation surface as the quadrate 
is still in position on the articular. The quadrate passes a short distance 
down along the outside of the articular. 
The connection between the prearticular and the articular is not quite 
clear, because this region is somewhat crushed. Apparently these bones 
meet on the inside of the articulation surface. From there forwards the 
prearticular rapidly becomes a very high bone, reaching its highest point 
behind the middle between the ossification centrum of the angular and 
the hinder end of the mandible. The upper edge of the hinder part of 
the bone, up to its highest point is covered by a bone of the skull roof, 
apparently the quadrate. From its highest point forwards the bone very 
rapidly decreases in height and becomes narrowest above the ossification 
centrum of the angular. Further forwards it becomes higher again until 
the front end of the infra-Meckelian vacuity is reached, whence it gradually 
diminishes forwards. The hinder portion of the bone up to its highest 
point looks inwards and downwards and the portion in front of its highest 
point inwards and upwards. The whole of the inner surface of the bone 
is covered with striae, which seem to radiate from a point somewhere 
below its highest elevation. 
There is no indication of an opercular in the parts preserved. If 
present it was situated further forwards. 
The complementary is a very long, slender bone. Unfortunately 
both ends are missing. It may have been in touch with the surangular, 
the hinder end of the preserved portion of the complementary, wdiich 
is situated a little in front of the junction of the dentary and 
the surangular lies on the upper edge of the dentary. Forwards 
it passes directly downwards on- the inside of the upper edge of the 
dentary. Opposite the last tooth in the dentary it is already lower than 
this edge. Further forwards, continuing along the inside of the dentary, its 
position becomes gradually lower. It is apparently wedged in between 
the dentary and the prearticular. The upper inner surface ol this bone, 
from a short distance in front of the hinder tooth of the dentary up to its 
front end as far as preserved, is covered with numerous minute teeth. 
As far as I am aware, this is the first time that these teeth are regarded to 
be on the complementary. In the preliminary description of these fossils 
this bone could not be identified with certainty and the prearticular was 
then regarded to be the splenial. A comparison, however, with the 
recently described lower jaw of Lystrosaurus (7) led me to the above 
identification of the bones. 
The supra-Meckelian vacuity is very long and broad. It reaches from 
below the last tooth on the dentary probably up to the articular. Its 
front end looks inwards and its hinder end upwards. The inner border 
behind and the lower border in front is formed by the prearticular. Its 
upper border in front is formed by the complementary and its outer 
border behind by the surangular. Perhaps a hinder border is formed by 
the articular. 
The infra-Meckelian vacuity is much smaller. Its hinder end lies a 
little further back than the front end of the supra-Meckelian vacuity. 
It is very long and narrow and bordered by the angular below and the 
prearticular above. 
