The Development of the Cartilaginous Skull ete. in Necturus. 433 
and the occipital cartilage, prior to articulation in the condyles. 
Sv6uR (80) states that he has not observed in Triton a continuity 
of cartilage preceding the atlanto-occipital articulation, which would 
make this articulation resemble that of a spinal arch. Gaurp (93) 
also says that he has not observed such a fusion in Rana. 
The skull in Necturus 46 mm long. 
The largest of the small Necturi which I raised measured 
46 mm, and were eight months old when killed. As the little 
creatures were raised from the egg in confinement, it is quite pro- 
bable that the stage of development does not correspond with that 
of the free animal of the same length. Moreover, the lengths here 
given are in any case of but relative value, since there is more or 
less individual variation among animals subjected to the same con- 
ditions of environment. 
I have made no drawing of a model of this stage, since the 
changes in the skull are not great and can be easily explained by 
reference to the model of the skull in the embryo of 19mm. The 
chief changes consist in the development of cartilage in connecting 
bars or plates found as procartilage in the younger embryo, and in 
the completion of the median wall of the auditory capsule and of 
the internal partitions which separate the floors of the anterior, 
posterior, and external semicircular canals from the main auditory 
chamber. 
The branchial cartilages have increased in size, and the pro- 
cartilage connecting dorsally the bars of the glossopharyngeal and 
vagus arches in the younger embryo has been converted into carti- 
lage. The trabeculae have become connected by an internasal plate 
near their anterior extremity, in the region indicated by broken lines 
in fig. 17. This plate is not an outgrowth from the trabeculae, but 
arises independently. It underlies the anterior part of the brain, 
and just beyond its posterior margin the olfactory nerve passes over 
the trabecula to the nasal epithelium, which is now supported by 
a narrow band of cartilage, that begins near the external opening 
of the nose and extends backwards over the dorsal surface of the 
nasal membrane, ending in a series of fine processes that reach 
laterally between the folds of the membrane. The nasal cartilage 
arises independently, as does also the cartilaginous ring that now 
surrounds the eye. This ring is but three cells wide and one cell 
deep. 
Morpholog. Jahrbuch. 25. 29 
