320 
HENRY ORR. 
rate cartilage is rather thin, and lies transversely with its 
lateral edge curved postei’iorly toward the otic cartilage ; 
farther ventralwards its section is shown in figs. 29 H and 30 h. 
The Meckelian cartilage shows no unusual peculiarities. An- 
teriorly it is connected with the cartilage of the opposite side 
by a short band of undifferentiated connective tissue. 
What the significance of this manner of development of the 
choudrocranium may be, or how much importance should be 
attached to it, I am unable to say, as I have observed it only 
at this one stage. 
At this stage well-characterised rudiments of teeth have 
appeared ( d ., figs. 30 h and 18). They are present in a semi- 
circle above the Meckelian cartilages. They do not appear in 
a single row, but in several irregular rows. In the same 
manner they appear just ventral to the trabeculae cranii along 
those parts of the trabeculaj which lie anterior to the optic 
nerve. In a cross section of the several irregular rows of 
teeth the teeth seem to radiate from the bar of cartilage on 
which they rest. In this respect the trabeculae cranii and the 
Meckelian cartilages present the same appearance. 
General Conclusions. 
The central nervous system of Amphibians first appears as 
a transverse epiblastic thickening dorsal to the mouth-fusion, 
and continuous with paired elongated epiblastic thickenings 
lying dorsally on each side of the median line. 
The primary cranial flexure is due to the presence of the 
transverse epiblastic thickening (anterior medullary plate). 
The transverse epiblastic thickening forms, when the brain 
is enclosed, that part of the brain wall which lies between the 
infundibulum and the optic groove (i. e. the depression just 
dorsal to the chiasma of the optic nerves). 
The first nerve-fibres which develope in the brain appear on 
what was originally the internal surface of the primitive epi- 
blastic thickenings running longitudinally in the dorsal region 
