Roy L. Moodie 453 
Sauropsida. The cones are not confined to the long bones, but occur in 
the ribs and all of the elements of the appendicular skeleton (Fig. 18). 
Parsons in his last article on epiphyses (10) draws a comparison between 
the conical ossification at the ends of the plesiosaur bones and the conical 
cartilaginous ends of the developing long bones of the pigeon. This com- 
parison is a new and interesting one and contains the key to an exact 
interpretation of these structures in the plesiosaurs. Such an appearance 
{Lr | [i 7m 
f.] I 
Ta I “i 
I Ne é 
t 
y 
Fie. 16. A section through the humerus of Amblyrhynchus. A= Bony 
epiphysis. B—=Endochondral bone which is less compact than the peri- 
chondrium. C—Medullary cavity partly filled with bone fibers. D—Com- 
pact perichondrium. 11% natural size. 
Fie. 17. A section through the tibia of Alligator. A==Large medullary 
cavity. BCone of endochondral bone. C=Perichondrium. % natural 
size. 
is not confined to the pigeon for I have noticed the cones of cartilage in 
the developing bones of the lizards, the turtles, and the chick. The cones 
are due to the mode of ossification in the Sauropsida, which is widely 
different from the method of ossification in the Mammalia. The forma- 
tion of the endochondral bone lags far behind the perichondral portions 
in the Sauropsida. The perichondrium is formed as a sheath around the 
