DEVELOPMENT OF THE SKULL IN THE BATKACHIA. 
75 
condyle looks more directly forwards, and not so much inwards ; the orbitar process 
is more elongated. 
The lower arches and labials (Plate 11, figs. 3-5, mk., I.I., c.hy., b.hy., b.br., h.br., 
c.br., ex.br.) are but little changed. 
17 (continued).—(C) Tadpole of Pseudis paradoxa, with all the legs large and free ; 
tail, 5 inches long ; its greatest width 1-^ inch. 
The chondrocranium (Plate 11, figs. 6, 7 ; and Plate 12, fig. 1), although relatively 
wider on account of the throwing out of the suspensorial bands, is only half the length 
it had, even in the second stage (B), and a third the length of that of the first (A). 
This temporary transitional form is very extraordinary ; I have caught no stage 
quite like it in any other species. 
The third Tadpole of Rana clamata (Plate 4, figs. 5, 6) comes nearest to it. The 
ethmo-nasal region, which was one-half the length of the skull in the last stage, is 
now less than one-third ; thus the orbital and auditory regions are now very large, 
relatively, and with them the cranial cavity is equally increased in size (relatively). 
The occipital condyles (Plate 11, figs. 6, 7, oc.c.) are now wider apart; but the ossifi¬ 
cation here is but little increased in extent. The bony substance has united over 
the occipital roof, and a definite tract of cartilage lies in front of the bone. There 
are no “ secondary fontanelles,” and only a wedge-shaped tract of the main fontanelle 
( fo .) is uncovered by bone (fig. 6). 
The notochord (nc.) is still present as a fine thread, and the basioccipital synchon¬ 
drosis is unaltered; moreover, the floor of the vestibule below, and the outer part of 
the capsule with the tegmen tympani, continue unossified. 
The semi-circular canals stand out strongly, and along the ridge of the posterior 
canal and part of the anterior ( pr.o ., au., ep.), the bone has undergone dehiscence, 
exposing the cartilage within, and partly separating the prootic from the ex-occipital 
on each side (fig. 6, pr.o., e.o.). 
In like manner, over the skull, the large frontals are partly severed from the small 
parietals (/., p.) ; the parasphenoid ( pa.s .), below, has become smaller (actually), and 
more elegantly formed. 
The unossified auditory floor (fig. 7) is now a more transverse, sub-oval mass, and 
the projecting, descending lip of the floor is very small (Plate 11, figs. 7 and 8 ; and 
Plate 12, fig. 1, fty.). The upper part of the auditory capsule projects beyond the 
vestibular pouch, very considerably. 
The cranial cavity lessens in width gently to the fore end ; the “ tegmen ” is of 
moderate extent over it, and part of it passes into the nasal region, as the roof of 
the ethmoid. 
The optic nerve (Plate 11, fig. 7, II. ; and Plate 12, fig. 1, II.) passes out of the 
hinder part of a large fenestra ; the roof-bones have a down-turned orbital edge. 
L 2 
