614 
MR, W. K. PARKER ON THE STRUCTURE ANT) 
This separation of the conjugatory or syraplectic region of the upper mandibular 
element is the exact morphological repetition of what takes place in the hyoid arch, in 
its relation to the mandibular, in the “ Chondrosteous Ganoids,” as Acipenser and 
Polyodon.. (See “ Sturgeon’s Skull,” ‘ Monthly Micr. Jour.’, June, 1873, Plate 20, fig. 1, 
sq. ; Traquair’s “Ganoid Fishes,” PartI.— Palceoniscidce —Pakeontographical Society, 
1877, plate 7, fig. 1, sq. ; and Bridge on Polyodon.) 
That is the last degree of specialization of these two post-oral arches in their 
relation to each other in the formation of a protractile and retractile mouth. 
In the Lizard the upper mandibular element becomes, as we have just seen, equally 
metamorphosed in relation to the parts above and in front of the mouth, the arrested 
palatine arch receiving copious supplementary growths from the pier of the mandible. 
In this (4 tli) section the upper and lower bands of the alisphenoid (al.s.) are cut 
through ; and below the lower bar the three branches of the trigeminal nerve (V) are seen. 
The surangular, angular, and articular (s.ag., ay., ar., MJc.), are shown in section 
below; the thick, proximal part of Meckel’s cartilage is not all ossified. 
The larynx lies forward on the long tongue ; thus we see the trachea ( trc.) lying over 
the basihyal ( b.hy.) ; part of the ceratohyal ( c.hy.) is shown further outwards. 
The 15 tli section (fig. 5) is through the fore-part of the tympanic cavity ( c.ty .), the 
Gasserian ganglion (V), the anterior semi-circular canal and its ampulla ( a.s.c .), and the 
wide part of the basisphenoid ( b.s .), where the basi-pterygoid processes ( b.pg.) are behind 
the cartilaginous facets. 
The prootic [pro.) articulates with the basisphenoid (b.s.) below the foramen ovale 
(V), and runs to a sharp edge above (see also Plate 43, fig. 8). The two bands of 
the alisphenoid (al.s.) are shown, and the lower of these is cut through where it lies in 
front of the ganglion (Y). The conchoidal quadrate (q.) is hollowed to form a recess 
for the drum of the ear; the tympanic membrane and the articular part of the jaw and 
the joint-cavity are shown ( m.ty ., ar.). 
But the drum of the ear, its parchment, and the rod that makes it tense, are better 
shown in the 1 6th section (fig. 6). 
The skull is here cut through in its hinder part, through the occiput; the super- 
occipital, joined to the epiotics (s.o., ep.), the exoccipitals (e.o.), and the broadest part 
of the basioccipital (b.o.), are shown. The canal cut through above is the posterior 
(below ep.), just behind its junction with the anterior ; the horizontal canal (h.s.c.) 
is cut across behind its ampulla (see also Plate 43, fig. 8). 
This fortunate section shows the relation of the middle to the inner ear, perfectly; 
under the “ tegmen tympani,” formed by the bulging of the horizontal canal, the 
columella is shown, its stapedial plate (st.) being cut across as it fits into the fenestra 
ovalis. 
The medio-stapedial bar (m.st.) runs outwards and a little downwards; one 
ossification served for this bar and the proximal plate (st.). 
This section can be conveniently studied with the details given in Plate 43, 
