454 Reptilian Epiphyses 
entire endochondral part. Brachet gives an account of the development 
of this cone of cartilage in the chick (11) and I think his account will 
apply to other Sauropsida. The cone of cartilage is first calcified and the 
calcified cartilage is subsequently replaced by bone. The formation of 
the endochondral bone takes place after the formation of the perichondral 
portion. The perichondral bone is what Lydekker in the plesiosaurs has 
called the shaft, and the endochondral pertion or the cones he has called 
the epiphyses. Both of these interpretations are incorrect. The cones 
or endochondral, and the sheath or perichondral portion together, form 
the diaphysis, and there is no epiphysis on the long bones of the plesio- 
saurs. The fact that the cones are separate from the perichondrium in the 
fossilized remains of the plesiosaurs is due, no doubt, to the fact that the 
Fic. 18. Photograph of the foot of a chick of sixteen days incubation. 
The cones of cartilage are clearly evident in the metatarsals and the pha- 
langes. 1144 natural size. 
endochondrium forms subsequent to the formation of the perichondrium. 
The perichondral sheath is almost fully formed before the endochondral 
cone starts to ossify. 
Brachet has fallen into the same misconception of the conical growth 
at the ends of the bones in the chick as did Lydekker in the case of the 
plesiosaurs. He calls the endochondral portion an “ epiphysis,” but it is 
not epiphysial in any structural sense for epiphysis means a growth upon 
and the structure in this case is certainly not upon, but within, the upper 
portion of the perichondrium. 
The cones or endochondrium in the plesiosaurs have been called epiphy- 
ses and have been used as a character on which to base the relationship 
of the turtles and plesiosaurs. The question of this relationship is an old 
one and has been discussed by various authors. But the presence of 
