464 Reptilian Epiphyses 
Howes and Swinnerton (13) make no mention of any epiphyses on the 
skeleton of the young of Sphenodon punctatus Gray, although they figure 
on Plate VI, Fig. 18, epiphyses on the foot. Albrecht, nowever, in 1883, 
called attention to certain structures on the neural spines of this form 
which he thought were bony epiphyses. So far as I am aware his state- 
ment has never been corroborated. I am not able to find any indications 
of epiphysial elements on an adult skeleton of this form, which is the only 
material available. The only element which might be called epiphysial is 
the olecranon. ‘This is free as in the Lacertilia. Epiphyses are not 
wholly absent from the skeleton of the Rhynchocephalians, and it is pos- 
sible that Albrecht is right. In his large work on fossil vertebrates (16) 
von Meyer figures a skeleton of Sapheosaurus on which there are quite 
evident epiphyses on the humeri and femora. The epiphyses are especially 
abundant on the lower end of the left humerus. 
Just why epiphyses should develop in some forms of the reptiles and 
not in others is a very difficult question to answer. They are certainly 
not essential to the formation of good articular surfaces since they have 
never been observed in either the pterodactyls or the theropodous dino- 
saurs. ‘These forms have a perfection of formation of the articular sur- 
faces such as is not excelled among the Sauropsida. In the fowl there is 
an epiphysis at the upper end of the tibio-tarsus and a larger one on the 
lower end. There is also an epiphysis at the upper end of the tarso- 
metatarsus. ‘lhe one at the upper end of the tibio-tarsus is undoubtedly 
a true epiphysis but the other two are more possibly elements of the tarsus 
which, in this case, may have an epiphysial appearance but are not true 
epiphyses (14). The two epiphyses at the ankle joint develop about two 
weeks after hatching and join with the diaphysis early. The other 
epiphysis is not formed until more than two months after hatching. In 
birds the articular surfaces are nearly as well formed as in the groups 
above mentioned, yet epiphyses are for the most part absent. 
It can be well understood how the aquatic and semi-aquatic reptiles, 
such as the mosasaurs, crocodiles, turtles, plesiosaurs and their allies could 
have dispensed with epiphyses, but it is rather difficult to understand just 
why they were not developed in the Pterosauria and Theropoda, and 
Seeley (25) mentions epiphyses as occurring in the former. 
The epiphyses which occur in the reptiles do not all have their origin 
in the same causes. Those on the ends of limb bones arise, undoubtedly, 
from different causes than do those which occur on the skull and girdle 
bones. Parsons calls the epiphyses at the ends of the limb bones “ pressure 
epiphyses.” ‘This nomenclature will hold for the higher mammals where 
