176 
ME. W. K. PAEKER ON THE STRUCTURE AND 
developed; for there is here no preorbital or lacrymal to set bounds to it*; it does not 
nearly meet its fellow on the broad, flat nasal cartilage ; just like the vomer below. 
The nasal is scooped where it lies above the external nostril, and then it becomes narrow 
where it joins the facial plate of the maxillary, and ends in a blunt-pointed preorbital 
process. The roof-bones of the skull (f.p.) have become thick, smooth, and bevelled 
towards the sagittal suture, which is persistent. Not so the coronal ; it is all oblite- 
rated save a small notch on the sagittal edge. These compound bones dip towards 
each other considerably; they are scooped behind above the prootics (pro.), to which 
the parietal portion is joined. Each parietal region diverges from its fellow behind, 
exposing the cartilaginous roof. The thick outer edge overlaps the cranial wall, and, 
descending, is scooped to form an “orbital process of the frontal” (Plate IX. fig. 3, 
and Plate X. fig. 8, f.). The parietal region is higher than the frontal. The rela- 
tion of the nasals and fronto-parietals to the endoskeleton is shown in the sectional 
views (Plate X. figs. 3, 7, 8, 9). The Frog is not much more liberally supplied with 
bony plates than the Lepidosiren ; for we everywhere find large bones occupying a 
double territory, if not taking the place of three. The so-called “ temporo-mastoid ” 
(Plate IX. figs. 1 & 3, t.) would seem to combine the supratemporal and preopercular 
of the Triton or of the Siluroid or Ganoid Fish ; it has also a process which repre- 
sents the “postorbital” of the Lizard. The manner in which the squamosal or supra- 
temporal bone applies itself to the protruded prootic is seen in the sectional view 
(Plate X. fig. 8, pro., t.). The descending portion speaks strongly for the subdivision of 
membrane-bones into parosteal and ectosteal ; for it is separated from the endoskeleton 
by a stratum of perichondrium, and, overlapping the quadrate bony plate, it is separated 
from it by a layer of periosteum (Plate IX. figs. 1 & 3, t., q.). 
The vomers (Plate IX. fig. 2, v.) are very elegant trifoliate plates of bone, wide 
apart, like the nasals, on account of the outspread form of the face, and correlative to 
the broad “subnasal laminse.” The middle leaf, which is emarginate, and the narrow 
falcate posterior leaf, together largely surround the internal nostril ; the pointed front 
leaf nearly reaches the suture between the maxillary and intermaxillary ; and the rounded 
stalk, which converges towards its fellow, is dentigerous. The “ septo-maxillary” (Plate 
IX. fig. 2, and Plate X. fig. 5) can just be seen between the middle and posterior leaflets 
of the vomer. 
The “ parasphenoid” has not lost its ichthyic dimensions (Plate IX. fig. 2, pa.); but 
it has become more elegant in form. The fore part is the “ rostral region” (r.) ; the trans- 
verse bars which undergird the expanded auditory masses are the “ basitemporal pro- 
cesses” (b.t.). The rostrum is subcarinate, the basitemporal plates are obliquely trun- 
cated postero-externally ; the median part ends behind the transverse bars, and supports 
the narrow unossified basioccipital cartilage (b.o.). Sections involving the parasphenoid 
are figured (Plate X. figs. 7-10 , pa.s.), and show the differentiation of a definite peri- 
chondrial layer between it and the endoskeletal basis cranii, from the ethmoid ( eth .) to 
* In the Bull-frog there is a lacrymal. 
