Roy L. Moodie 465 
there is a distinct pressure on the limbs but in the case of the majority of 
lizards, this pressure is not directly transmitted through the axis of the 
limb since the limbs are set, often, at angles from the body of from ten 
to sixty-five degrees. In the chameleons, which are to a large extent tree 
dwellers, the nearest approach to the mammalian attitude is attained and 
im these the epiphyses may be due to pressure. But in Amblyrhynchus, 
which spends a part of its time in the water, there are more epiphyses 
than there are in the chameleons and the limbs are set at much wider 
angles from the body than is the case in the chameleons. I am of the 
opinion that the epiphyses developed on the limbs in the majority of the 
Lacertilia are not due to pressure directly but that they arise from other 
and as yet unknown causes. It is possible that they are developed from 
both pressure and traction, but we need further evidence on this point. 
Some of the epiphyses of the skull can be accounted for by the fact 
that in certain forms the elements of the skull atrophy and their remnants 
are left as scales of bone which resemble epiphyses, and in these cases 
could hardly be distinguished from epiphysial structures. Such a case of 
an atrophied bone is cited by Baur in the Geckonidae (15). The epiphy- 
ses which occur elsewhere on the skull and on the girdle bones may pos- 
sibly be due to the strain or pull of muscles, but this is doubtful. If they 
do arise in this way then it must be conceded that the stuctures which sub- 
sequently develop into epiphyses must first be cartilage, then calcified 
cartilage and then bone. Whether such is the mode of origin of the 
“traction epiphyses” or not is still to be settled. If this should be 
claimed to be the case then might we not expect that in time the sternum 
of the Lacertilia would become osseous. As far back in geological time as 
we know anything about the sternum of the lizards or their relatives, it 
has been merely calcified cartilage. Surely the millions of years which 
have elapsed since the time of the early Lacertilia of the Cretaceous have 
given ample time for the sternum to become bony, but it is no more bony 
now than then. For this reason and for others it is to be doubted whether 
a structure can develop independently from calcified cartilage into bone 
although calcification is a part of the process of ossification in some forms. 
The epiphyses on the carpals and tarsals of the lizards must be the 
degenerate elements which have become united with their fellows. This 
is certainly the case in some forms, but in others it is doubtful if this 
explanation will hold. 
What the causes are which have produced epiphyses, I cannot say. It is 
possible that Parsons’ explanation of the pull of muscles and the pressure 
of the body are the correct ones. So far this is merely a matter of opinion. 
