462 Reptilan Epiphyses 
It is interesting to note the method of development of the epiphyses 
in the lizards. As above stated there are no epiphyses present in the 
embryos of the lizards so far as I am able to determine. In the embryos 
of Cnemidophorus there is not a trace of epiphysial structures in the 
articular cartilages of the limb bones. In a young Sceloporus, the epiph- 
yses are just appearing as minute points. In the adult Sceloporus the 
epiphyses are indistinguishably united with the diaphyses. This seems 
to be the usual life history of the epiphyses among the Lacertilia. But 
to this there are some notable exceptions. In the young of Chameleon 
owenwt Gray, there are in a young specimen, two inches in length, no 
epiphyses present in the hand or foot. The epiphyses in the hand and 
foot of the adult are quite large and do not unite at all with the diaphyses, 
but remain much more distinct than I have ever seen them in any 
mammal. I do not possess young stages of the Heloderma, but in the 
young of Amblyrhynchus and Varanus the epiphyses separate easily from 
the diaphysis and this is especially true of the Varanus. In the adult 
forms of this genus the epiphyses are closely attached but do not fuse 
with the shaft. 
From the above facts it will be clear that the method of development 
of the epiphyses in the Lacertilia is not at all uniform. In some lizards the 
epiphyses are more evident in the young; in others they are more evident 
in the adult. Whether these facts are of any particular significance or 
not remains to be determined. At any rate it is clear that the presence of 
epiphyses in the Lacertilia is a very variable matter and one would be 
inclined to the opinion that they may occur at any place on the skeleton 
where there is strain or pressure. Epiphyses are to a certain extent 
sesamoid, but are not sesamoid bones in the ordinary meaning of that 
term. 
One of the most interesting facts in regard to the epiphyses of the 
Lacertilia is that they are never found on both ends of the phalanges. In 
none of my specimens is there the slightest indication of an epiphysis on 
the distal end. They occur always on the proximal end. In the mammals, 
with the exception of the Cetacea, the same condition is found. They are 
present only on the proximal end of the phalanges in both groups. Per- 
haps this is another case of parallel evolution, but it doubtless has more 
significance than that. It seems to me that the epiphyses and their 
arrangement is a matter of some importance in the phylogeny of the 
vertebrates. Not that they can be of much taxonomic importance, but 
that they are significant of primitive conditions. It has always been 
assumed by anatomists that epiphyses were developed first in the mam- 
