The Development of the Cartilaginous Skull ete. in Necturus. 417 
bars are not united with one another ventrally, but are connected 
dorsally with the basicranial plate. The mandibular bars are separate 
from one another ventrally and are also separate from the basieranial 
plate; they extend, however, dorsalwards to the horizontal plane of 
this plate. In fig. 8, pl. XVII, the procartilage of the mandibular arch 
is seen in side view. The quadrate, which appears almost separate 
from the procartilage of MmcKEL’s bar, is, however, united with the 
bar by means of closely grouped mesectoderm cells that fill the 
space between the dotted line, seen in fig. 8, and the surface of the 
bar. Although these cells are not as yet differentiated into pro- 
cartilage, they ultimately form cartilage. 
The remaining branchial procartilages may be said to lie in one 
transverse plane, so slightly do the bars curve upwards. ‘This plane 
is removed from that of the brasicranial plate by a distance equal 
to the length of the median bar between the procartilage of the 
hyoid and glossopharyngeal arches. The hyoid procartilage consists 
of a single curved bar united in the centre to a median longitudinal 
bar that forms a cartilage which Fischer ('64) calls the »body of 
the hyoid«, and which Huxuey (’74) distinguishes as the »first basi- 
branchial« in Menobranchus (Necturus). This designation is also 
applied by SröHr and WIEDERSHEIM to the corresponding cartilage 
in other Urodela. 
The procartilage of the glossopharyngeal arch is also a single 
eurved bar. Posterior to the centre of the bar there is a knob of 
tissue that develops into the Zungenbeinstiel of Fiscuer (loc. 
cit.) or the second basibranchial of HuxtLey and WIEDERSHEIM 
(loc. cit.). The development of the glossopharyngeal cartilage does 
not support FISCHER’sS view that the bar in Menobranchus (Nec- 
turus) contains elements from two arches, since the cells that compose 
it belong from the first to the third branchial arch alone. 
The bars of the vagus arches do not meet in the median plane, 
but the bars of the first vagus arch extend backwards from the lateral 
part of the glossopharyngeal bar, while the bars of the second vagus 
arch extend backwards from those of the first arch. 
The differentiation in the mesoderm at the side of the chorda 
which forms the basicranial plate is not sharply limited either laterally 
or posteriorly. It gradually becomes apparent anterior to the first 
Spinal nerve. This nerve, which possesses a ganglion, but has merely 
a ventral root, lies median to the third myotome (4'" postotic 
segment). The procartilage of the occipital arch (fig. 7) rises from 
Morpholog. Jahrbuch. 25, 28 
