426 Julia B. Platt 
the plate is evidently unsegmented. This fact should not be regarded 
as supporting the view of GEGENBAUR (72), GoErTE (75) and Wik- 
DERSHEIM (77) regarding the elemental unity of the basal plate of 
the skull. The procartilage of the branchial arches is also unseg- 
mented, although each cartilaginous arch, except the posterior, is 
composed of distinet segments. The relation of procartilage to carti- 
laginous segmentation, is similar to that of the axial mesoderm to 
metameric segmentation. Both tissues supply the unsegmented ma- 
terial on which the future segmentation is stamped. 
In the Anura, Srénr (82) tells us, there exist in the basal 
plate of the skull at an early stage of development, three pairs 
of thicker cartilaginous elements, which are at no time completely 
separate, being from the first connected with one another by thiner 
tracts of cartilage. The anterior pair of cartilaginous elements are 
the trabecular plates, the median pair, Srönr calls the »mesotic« 
cartilages, while the posterior pair are the occipital plates, the 
»parachordalia« of HuxLky, or enlarged bases of the occipital 
arch. In the cartilage which in Triton connects the auditory capsules 
with the axial part of the basal plate, Sréur finds the homologue 
of the mesotic elements of the Anura. 
In the development of the basal plate, Necturus occupies, in 
some respects, an intermediate position between the Urodela described | 
by Sréur (Triton and Siredon) and the Anura. As in Triton, 
cartilage first appears in the trabeculae, then in the occipital 
region, extending from these Anlagen through the intervening space. 
Unlike Triton, however, in Necturus, these cartilaginous elements 
are not at first distinctly separate, but as in the Anura, the primitive 
Anlagen pass into one another, so that there is actually but one 
pair of plates, separated by the chorda. 
The cartilage of the auditory capsules arises independently in 
Necturus, and parachordal cartilage is not associated with the 
periotic in the formation of the floor of the capsule. PARKER (’76) 
also finds the otic capsule in the Urodela independent of the basal 
plate, and Gorrre (75) claims that this in the case in Bombinator, 
but GAurp (’93) tells as that in Rana, the floor of the auditory 
capsule is in part formed from parachordal cartilage. 
The first procartilage of the auditory capsule, as shown in 
Part I, arises in tissue continuous with the mesothelium of the hyoid 
areh, seen at an early stage in fig. 11, pl. XVIII. In the later develop- 
ment represented in fig. 12, this mesothelial tissue is separated into 
