DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
199 
touching all these points of the hind skull would form part of a very large circle, and 
this arc would be sub-equal to that formed by the cheek and jaw bones, right and left. 
The muzzle is very wide, but its arc would form part of a circle only half the size of 
the one just supposed. 
A semi-circle finishing the lateral outline would make the form into an ovoid. 
A rather narrow tract of cartilage divides the right and left bony masses of the 
hind skull, but the prootic is confluent with the ex-occipital (cm., e.o.). This common 
bony mass reaches beyond the horizontal canal, externally, and in front runs up to the 
optic fenestra (II.), enclosing the foramen ovale (V.). Most of the cartilaginous 
tegmen tympani (t.ty.) is covered by the large ear-shaped temporal plate of the 
squamosal ( sq .); its rounded hind part, however, is naked. 
The epiotic eminences (ep.) are wide, they are not covered by the roof bones, but 
much of the anterior, and the ampulla of the horizontal, canal, are covered, for the post¬ 
orbital process is broad, and unites by suture with the squamosal. The endocranium 
in the orbital region is much overlapped by the roof slabs ; it is of nearly equal breadth 
before and behind, and is gently narrowed behind the middle. 
The girdle-bone (eth.) takes up three-fifths of this territory, and does not finish its 
own wings; but it sends forwards a short median and a pair of lateral bony growths 
under the nasal region (fig. 2, etli., s.n.l.) ; its margins are sinuous. The unossified 
wings of the ethmoid are segmented from the ascending process of the palatine 
cartilage (fig. 3, e.pa.) ; they are very solid, and in front are continuous with the broad 
subnasal laminm (fig. 2, s.n.l.). These laminae end in front in dilated horns ; the inner 
cornua, or pro-rhinals ( p.rh.), are conical, and turn inwards. The snout is transverse, 
gently emarginate, and moderately broad ; from its angles a narrowish band of cartilage 
runs backwards on each side, these are confluent, behind, with the wings of the 
ethmoid: they are the arrested nasal roofs (n.r.); between them and the widened 
top of the septum (s.n.) there is a large crescentic fontanelle (or fenestra). 
The first and second labials (u.l l .u.l z .) are well developed; the second nostril-valve 
is very large and solid. The palato-suspensorials are so modified as to form the 
type of a sub-group—the Bufonine, as distinguished from the Ranine. Primarily, as I 
have shown in a former paper (“ Batrachia,” Part II., Plate 54, p. 607), the development 
of these parts takes place as in Rana, but their metamorphosis is much modified. The 
bony plates here use up much of the cartilage, which remains as an ethmo-palatine 
(tig. 3, e.pa.) jointed off from the ethmoid above and free below, exactly, now, like that 
of a Skate or a Salamander. The pterygoid cartilage also (fig. 3 , pg.) is now, as in 
those types, quite free from the ethmo-palatine, and is, what we find in Selachians, in 
young Teleosteans, and in Urodeles—merely a symplectic process of the suspensoriurn 
of the lower jaw. 
The palatine bone, also (pa.), is composed of two parts : the normal ectosteal plate, 
and a sub-distinct knife-like crest, which is very sharp and steep; the old remnant, 
undoubtedly, of a dentigerous plate, like the palatine bone of a Urodele. 
