DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
647 
trough, which has a thick cartilaginous rim, is filled up by the inner inbent part of the 
interstapedial. 
The trough and the fenestra were forming in the first stage (Plate 56. fig. 5 ,fs.o.) ; 
the stapes was developed in the second (Plate 57. fig. 2, st .) ; but in the fourth stage 
(Plate 58. fig. 3) there was no cartilaginous “ columella,” the differentiation of which is 
very late ; and this element, although correlated with, is evidently not a part of the 
stapes. 
Certain dee]) laminae of fibrous tissue which had undergone ossification have been 
described as part of the largely ossified chondrocranium. Of these the pterygoid and 
articulare have largely used up the cartilage to which they were applied and related ; 
but one of these plates, contrary to the wont of the Batrachia, has failed to do so, 
namely, the “ superethmoidal ” (figs. 1 & 3, s.eth.). I class it, however, with the endo- 
skeletal bones in this group. Its counterpart in Bony Fishes may or may not attack the 
cartilage. Another bone, the quadrato-jugal, is a mere splint in the Saurojjsida, but is 
a grafting-bone in the Batrachia. I think it better to keep it amongst the “ investing 
bones,” which are ossifications of shallow laminae of fibrous tissue. 
The first of these outer bones to appear was the parasphenoid (joa.s.), and it is now 
the most remarkable. This bone (fig. 2) reaches nearly to the foramen magnum behind, 
and almost to the premaxillaries in front. It is the perfect miniature of a straight sword 
with a blunt tip. 
Protecting the under face of the blade of this bone, near its tip, is a small, transverse, 
bony shield, the vomer ( v .) ; azygous only in this kind of Batrachian as far as I know 
(see “Frog’s Skull,” plate ix. fig. 2, v ); here it has a rounded front and hind margin, 
and a rounded lobe on each side. In the notch between the front and side there is a 
strong ligamentous band which attaches it to each premaxillary. 
The nasals (figs. 1, 3, n .) are small crescentic bars, lying on the hinder face of the 
large labial pouch ( u.l .), and attached by their broader inner end to the second small 
labial ( u.l. b ). 
Together, the premaxillaries and maxillaries (px., mx.) form an elegant arch, the 
two former being the keystones ; these have a sinuous palatal process (fig. 2) below, 
and a trifoliate nasal process (fig. 1) above. The maxillaries (mx.) are thickish, gently 
curved bars, rounded above and scooped below ; the whole series is dentigerous, and 
the maxillary teeth run back four fifths of its length. The jugal, non-dentigerous ends 
of the maxillaries end at an imaginary transverse line drawn through the middle of the 
skull. 
Behind the interlocked junction of the maxillaries and premaxillaries, there is a seed- 
like ossicle ; it lies on the neck of the great labial pouch ; this is the “ septo-maxillary ” 
( s.mx .). 
Over the great fontanelle (fig. 1, fo .) there now lies a huge slab of bone, which has 
shelving sides and ends, and a ridged top, like a “ ridge-tile it reaches from the middle 
of the superethmoidal bone (s.eth.) to near the verge of the foramen magnum : this is 
