DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 95 



The difference between this skull (figs. 8, 9) and that of the lesser of the two large 

 Tadpoles is slight, indeed, but there are noticeable modifications. The occipito- 

 auditory regions are more developed, and the parts more fused ; the fenestra ovalis 

 ( /!o.) is larger and wider open, and more lateral in position ; but there is no stapes. 

 The interorbital part of the skull is of the same shape, and so is the great fontanelle 

 {fo.). The ethmoidal region is in the same unfinished condition, but the cornua 

 trabeculse {c.tr.) are a little shorter, and the thick edge below is less st)lid, but it creeps 

 roiind to the inner edge. Also at their root the cornua have a small snag for attach- 

 ment of the membrane in front of the internal nostril [i.n.). The ribbed edge of the 

 orbitar process {or. p.) is extended further back, as a strong decurrent enlargement, 

 nearly to the apex of the pedicle {pd). 



The pre- and post-palatine rudiments (the snag inside q., and yt.pa.) are much 

 alike in both species; so are the mandibles [ml:), the lower labials (l.l.), and the 

 cerato-hyal [chi/.). But the upper labials {■u.l".u.V'.) differ; the right and left inner 

 pair are united in front, and all four are rounder and broader ; here we get nearer the 

 Lamprey. 



The fronto-parietals (fig. 8,f.p.) are large, and moreover they have a sigmoid, and 

 not a straight, form. 



But the parasphenoid (fig. d, pa.s.) is the true generic diagnostic; it is more split 

 than in the younger Tadpole of the other species ; the notch and the two sharp 

 blades being one-fourth longer than the united part, which has more distinct lateral 

 processes. 



If we reflect upon the short time in which this bone changed from what is figured 

 in fig. 2. to what is shown in fig. 6, it will occur to anyone that there is strong reason 

 to believe that, for a short time, each "trabecula" had its own investing bone. In 

 the Chick, about the middle of the second week, the hinder parasphenoid (" basi- 

 temporal") is composed of a right and left osseous centre (Phil. Trans., 1869 ; Plate 82, 

 fig. 2, h.t.). 



The great constancy of this bone as an azygous basi-cranial splint in the Ganoids, 

 Teleostei, Dipnoi, Urodela, and in most of the Anura, makes one surprised to see it 

 with its apex bitten off in Rana pipiens and R. haleciua; it would not be more 

 remarkable to find it modified by median division, also, and here this seems to be 

 the case. 



21. Cysti(jnathus ti/phoniua. — Adult female ; 1^ inch long. Porto Rico. 



This small species has a much more ossified skull than the last large kind, just as 

 the skull of the small Cyclovhamphus marmoratus (Plate 20, figs. 1-3) is much 

 stronger than that of the large C. cideus, as Mr. Garman has shown. 



On the whole this skull is very similar to the last, but its occipital condyles 

 (Plate 16, figs. 6 and 7, oc.c.) are wider apart. The epiotic prominences [p.s.c.) are 



