DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
241 
The roof runs on for a third the length of the cranial cavity, but it has two lesser 
fontanelles (fig. 7) in it; the main fontanelle is very large and heart-shaped, the 
front and side growths of the tegmen cranii being slight. The generalised occipito- 
auditory bones leave the very limited and rounded tegmen tympani (t.ty.) soft; in 
front, the bony matter forms a good margin in front of the foramen ovale (fig. 8, V.). 
Then more than half of the orbital walls are cartilaginous (o.s.), and in the middle of 
each space is the rather small optic fenestra (II.). 
The girdle-bone (fig. 8) is in rudiments right and left, and there is no mesethmoidal 
bone. Each bony tract is composed of a large cochleate cranial part, separated by half 
its width from its fellow, and perforated by the orbito-nasal nerve. To this part there 
is a handle growing out at more than a right angle, and ending in an adze-shaped 
dilatation (fig. 8, pa,). 
The fact is that the arrest of the bone towards the middle—above and below—is 
accompanied with an overgrowth beyond the proper alse of this region, and the whole 
palatine tract, which has no ectostosis of its own, has become ossified from the ecto- 
ethmoidal, so that its three regions, ethmo-, pre-, and joo.st-palatine, are all used up to 
form the handle to this curious “ lateral ethmoid.” The well-developed roof and floor 
of the nasal region (figs. 7 and 8) are entirely unossified ; there is a short prenasal (p.n.), 
the nostrils (e.n.) are almost tubular, and are defended by the normal valves (u.V-.u.V 1 .). 
Below, the internal nostrils (i.n.) are very wide apart, because of the breadth of the sub¬ 
nasal laminse (fig. 8); these end in broad ear-shaped angles, outside, and near the 
middle have small apiculate pro-rhinals (p.rh.). 
The pterygo-quadrate region is feeble, and the well-shaped, and distinctly-jointed 
pedicles ( pel .), are a long distance apart. The pterygoid-bone (y>p.) has not ossified 
all the cartilaginous band (fig. 7); its forks are very short. The quadrate is partly 
ossified by the quadrato-jugal, and the condyles (q.c.) are oblique, and well-formed, 
with the hinder lobe of the trochlea much the larger. The Eustachian passage ( eu .) 
is oval, and half the normal size. The annulus (fig. 11, a.ty.) is normal; its horns do 
not meet. 
The stapes (figs. 7, 8, 11, and 11a, s£.) is, relatively, the largest known to me, and it is 
also the hollowest, being like an oval Limpet-shell; on its top is an oblong boss, and its 
substance is sub-osseous, except in front for a small space : the calcification is passing 
into true ossification over most of it. The columella is in one piece; a considerable 
cartilaginous lobe passes within the stapes,- and then it forms an arched rod, the medio- 
stapedial ( m.st .); the extra-stapedial (e.st.) is peltate, and has a small rudiment of the 
supra-stapedial band. The lower hyoid bar has not quite lost its larval solidity; the 
stylo-hyal end (fig. 8, st.h.), is massive, and is only partially confluent above. The 
rest of the bar (fig. 10, c.hy.) is narrow, and only dilates a little in returning to the 
basal plate ; over the bend, an “ extra-hyal ” band is separated ( ex.liy .). The notch of 
the basal plate is large, the form wide, the lobes only moderately free : a thick crest 
occupies the middle of its lower face, this expands in front, and is calcified; behind, 
MDCCCLXXXI. 2 I 
