504 SAODILE S| TAO Te SAMOLD EAN TES, 
and the posterior ends the bore is still full size; this tends to 
divide the notochord at the middle of each vertebra and to 
leave intervertebral segments. This condition of the vertebre, 
with deep cups at each end, is called “biconcave.” It is the 
same condition that is found in the primitive reptiles, and the 
closing of the notochordal canal and the filling up of either the 
anterior or the posterior cups of the vertebra would complete 
the development of the highest type of the reptilian vertebra. 
(Eigen woe) 
Fic. 1.—A Section of Branchiosaurian vertebree showing size of notochordal 
canal; # Section of microsaurian yvertebree showing contraction of notochordal 
canal. 
Another type of vertebree that was developed by the amphib- 
lans seems to be somewhat more primitive than the last 
described, and also to be somewhat off the line of direct devel- 
opment. There were four distinct pieces, an upper, that sup- 
ported the spinuous process, a pair, of small size, that stood on 
each side of the notochord, the pleura-centra, and a crescent 
shaped piece on the lower side, the intercentrum, that occupies 
the position of the plate supporting the hamal arch in the 
simpler vertebree. Upon the condition of these four pieces were 
established the divisions of the suborder Labyrinthodonta vera. 
When the pieces are all separate and in the condition described 
above, the forms are called rachitomous; the two lateral 
pieces may fuse and form a ring around the notochord, and 
at the same time the intercentrum develop from a crescent- 
shaped piece into a perfect ring, so that each vertebra is repre- 
sented by two complete rings, this is the embolomerous stage ; 
in the third condition the four pieces fuse to form a solid ver- 
tebra; this is most common in the caudal region and may be 
present there, while in the anterior portion of the column the 
