DEVELOPMENT OF THE SKULL OF THE COMMON FROG. 
157 
in the third stage (Plate III. fig. 3, Plate IV. figs. 1 & 7, ctu.) ; it is now open again, for 
a long-oval segment has been as it were cut out, and yet left in, like a miniature bung ; 
this is the “stapes” (Plate V. figs. 1, 2, 4, 6^.), and the opening is the “fenestra 
ovalis its situation is infero-lateral, and is .nearly midway between the ends of the 
capsule. 
The “ glosso-pharyngeal nerve ” escapes near the end of the capsule below (fig. 4, 8"), 
and the “vagus” (S 4 ) between it and the occipital cartilage ; the ganglion of the fifth 
nerve (5) lies close to tli e prootic region, opposite the end of the notochord, and sends 
its branches over the metapterygoid connective (m.pg.). 
The portio mollis (7 A ) enters the capsule below the junction of the anterior and pos- 
terior canals (fig. 3, a.sc., ps.c., l b ). Posteriorly, the epi otic .-region (ep.) framed upon 
the posterior canal (p. sc.) projects nearly as far backwards as the now well-formed occi- 
pital condyles (o.c.). 
The notochord (n.c.) has now become very much diminished (figs. 3-5), and is bridged 
over by the investing mass (i.v.) behind. It has relatively retreated in front, leaving an 
open fissure, the “ posterior basicranial fontanelle.” 
Having described the face and skull from lateral and horizontal views, and from a 
longitudinally vertical section, I must describe the transversely vertical sections. This 
will involve some repetition, but a much more perfect idea will be obtained of the 
relation and thickness of the parts ; the reader must keep the other views before him 
if he would understand the numerous sections. 
Two things will be noticed at once in these views, namely the thickness of the “derm,” 
and the large quantity of subcutaneous gelatinous stroma in which the more solid organs 
are enveloped. 
The first transverse slice of the face (Plate V. fig. 6) has already been described ; the 
second (Plate VI. fig. 1) shows the form of the oral opening ( m ), and exposes the nasal 
tube (ol.) both near the skin and also near the trabeculae, which are shown in their 
relation to the fore part of the palatal region. A pair of papillae are seen lower down, 
projecting into the mouth, the floor of which is a deep angular fossa. 
The clubbed ends of the Meckelian rods (mlc.) are cut through on each side; and a 
vertical section has been made through the lower labials ( l.l .), the form and relations 
of which are well shown ; they are invested below with the lower dentigerous plate 
( l.d.g .); and on each side the smaller teeth of the labial rugae (Ip.) are also shown. 
This is the back view of a solid slice of the face ; and the next (Plate VI. fig. 2) is 
the front view of another slice made further backwards. This section is still in front of 
the “ trabecular commissure,” and lays open a reduplication of the nasal sac (ol.). 
Here the Meckelian rods (mlc.) are completely displayed up to their condyloid fossa, 
and the lower labials (l.l.) are seen, as also the lower dentigerous plate and labial den- 
tigerous rugae ( l.dg ., Ip.). 
The posterior face of the next slice (fig. 3) displays the trabeculae in the ethmoidal region 
(eth.) immediately behind the commissure ; the rhinencephala (C 1") are cut through. 
