DEVELOPMENT OP THE SKULL TX TUK BATRACHIA. 2") 



Imrny plate, convex outside and concave within, but also lesser denticulate horny pro- 

 ductions (a ?\) on the outer folds of the lips, and numerous thick papilla? (o.^.), laterally. 



The main horny plate (Plate 1, fig. 3) forms a sheath to the upper labials {n.l.) ; 

 behind this the mucous membrane is seen as a bilobate cusliion, marked off behind by 

 a deep sulcus which runs from one quadrate hinge {q.c) to the other. 



Behind this sulcus the mucous membrane is raised into a second cushion, which is 

 concave in front, and which passes backwards into the large palatal roof. At the mid- 

 line its foremost third is marked off by an "anterior palatal velum" [a.v.) ("median 

 triangular papilla" of Huxley, op. cit., p. 429); this is covered with small papillae, 

 is semi-oval in shape, and is curved forwards ; its attached edge is crescentic, the 

 convexity looking backwards. 



In front of this flap there are two long clefts (in.) which approach each other at the 

 mid-line, and then greatly diverge, forwards, nearly reaching the exposed quadrate 

 hinge (q.). Each cleft is lipped in front, and this lip runs back again along the cleft 

 dividing it into two chinks ; this apparently double slit is guarded by two lai-ge 

 papillse : it is the internal nostril. In the chondrocranium this passage appears as a 

 large round hole between the trabecular cornua and the quadrate (Plate 3, figs. 1, 2, 

 i.n., c.tr., q.) and only partially enclosed by cartilage in front. I have just described 

 these parts. 



At the sides, opposite the " anterior velum," the condyle on the fiuspensorium for the 

 hyoid cornu is exposed {hy.f.). 



The interorbital region of the palate is lower than either the internasal or the inter- 

 auditory ; it is one-fourth longer than broad, is covered with papillae, and has the 

 largest of these productions postero-laterally. 



The hind part of this palatal tract is, properly speaking, yawciai; it is beneath the 

 ear-sacs, and reapplies the basioccipital region. This is separated from the proper palate 

 by two " posterior vela " {2^-v.) ; these are crescentic folds of mucous membrane, with 

 their convexities forward, or opposite to that of the " anterior median velum " {a.v.). 



The floor of the mouth is shown from above (fig. 4) ; the free mandibles {mh.) and 

 the hyoid cornua {chij., hy.c.) have their upper or articular ends exposed. 



The inferior horny jilate, with the outer denticles of the folds of the lower lip 

 (Plate 1, fig. 4) are shown, as well as the right and left crops of labial papillae ; the 

 main horny plate is modelled on the horse-shoe shaped lower labials {I.J.). 



In this view all tlie post- oral clefts are seen, for at present the pouch-shaped 

 (blind) first cleft (c/'.) is low in position. I have found it open externally in no stage, 

 although the skin over it is very thin at the time of hatching. (See my first paper 

 on the "Frog's Skull," Phil. Trans., 1871, Plate 3, fig. 10, c/'.) 



This low position of the first cleft is due to the extreme length and horizontal 

 position of the "pier" of the mandibular arch (see Plate 3, figs. 1, 2), the hinge of which 

 (fig. 1, q.) nearly reaches the upper lip ; afterwards, in the adult, it is beneath the ear. 



This cleft (Plate 1, fig. 4, cV.) is small, crescentic, and with its convexity looking 



MDCCx::'Lxxxi. e 



