412 HARRIS HAWTHORNE WILDER ON 
evident and presented a similar appearance in a series taken from a larva of 26 mm. This 
observation, which seems perfectly clear and unassailable, and which corroborates the 
results given by Stéhr in other Urodeles, is absolutely at variance with the statement of 
Miss Platt, who says that “it arises independently ” and identifies as its anlage a mass of 
cells which, in an embryo of 19 mm., is situated just in front (outside) of the fenestra 
ovalis, and between it and the end of the ceratohyal. It is possible that this anlage 
may represent a true columella or hyomandibular cartilage, which may later become 
fused with the true operculum to form its projecting external process, although in 
the larvae of 26 mm. and 44 mm., the series which I have examined, I can find no 
trace of such a double origin of the parts in question. 
The brain case.— This is formed in great part by five dermal bones, the two frontals, 
two parietals, and the parabasale, of which the first four form its dorsal, lateral, and ante- . 
rior walls, and the parabasale its floor. The box formed by these is deficient poste- 
riorly, where it is completed by the otic capsules and other cartilaginous elements with 
their ossified areas. Above, each 
frontal is so completely welded to 
ined “Vv its accompanying parietal by means 
; of interlocking splints that they practi- 
cally form one bone while the two sets 
a6Na x PB (= uncinate proces of united pairs meet in the median 
of Frontal ) : 5 A 
line by means of somewhat thickened 
flat edges, forming symphyses. Upon 
Ht es ties °F the ventral surface of this roof, both 
rabeeulae. (ouficle 
stavicte) bones end down extensive processes 
iB 
sae eae Ae that lie just within the trabecular 
arch of the primordial skull and make 
an extensive ridge in the form of a 
long narrow U, the loop being directed 
Pine Gite anteriorly. This ridge forms the 
ridge is_ reingorced 
front and sides of the brain case and 
by @ precess from é Vie 22> 
reteset: G/ f {e “: at its ventral edge is everywhere 
in contact with the parabasale. 
The result of this smgular forma- 
Fig. 12. The roof of the brain case seen from beneath. 3. 
: : : , 5 
This is composed of the two frontals and the two parietals, upon tion is that in Necturus the lateral 
the ventral side of which is developed a series of processes which walls of the brain case are formed of 
together form a U-shaped ridge that forms a front and sides to : +p 
solid dermal bone reinforced exter- 
the case. Contact surfaces for other bones are designated by an 
x and the abbreviations of the bone involved. nally by cartilage while in most Uro- 
