DEVELOPMENT OF THE SKULL IN THE BATllACHIA. 181 



cranium in the " Hylide " is very characteristic ; the stoutness of the larval skull 

 gives no promise of the delicacy of structure shown in that of the adult. The skull 

 at this stage con-esponds very closely with that already described (Plate 30, figs. G, 7) 

 in the larva of a narrow-backed Tree-frog, viz. : Acris Pickeriiigii, a type not very far 

 removed from the Oxydactyle " Cystignathidte." 



Up to the quadrate condyles (Plate 30, figs. 8, 9, 7.) this is a rather square skull, 

 but those hmges are further back than in any other kind known to me, rcacliing very 

 little in front of the inner nostrils ((•».) ; the cornua trabeculte, on the other hand, are 

 so long as to make this really one of the longest of the Tadpoles' skulls. 



In this skull the occipital arch is fully formed, and the notochord (uc.) has become 

 very small ; the condyles {oc.c.) are perfect, and the tegmen cranii (fig. 8.) runs forwards 

 as far as to the exit of the 5th nerve (V.). 



The large auditory capsides («''.) reach as far back, nearly, as the condyles; and 

 their breadth is about as great as that of the intermediate basal plate. Externally, 

 they reach nearly as far outwards as the suspensoria, for the tegmen tympani (t.ti/.) is 

 already developed outside the horizontal canal {Ji.s.c). In front of the tegminal lobe 

 there is a smaller lobule of cartilage ; here the formation of this tissue is spreading 

 over the opercular region of the 1st cleft; that lobule will be detached as the 

 "spiracular cartilage" (.yxc). The fenestra ovalis (fig. 9) is formed, but the stapes 

 (st.) is not chondrified. The mterorbital region is one-foui'th longer than the inter- 

 auditory ; apparently the basal plate is of the same width, but the wings that form the 

 auditory floor are not evident at fii'st. From the point where the notochord was, to the 

 projection on each side in fi-ont of the inner nostrils {i.ii.), the trabeculee [tr.) are very 

 uniform in width. There is an evident tract of newer cartilage (intertrabecular) from 

 the point where the notochord ended, to the most contracted part of the trabecular 

 (fig. 9, tr.) : and above (fig. 8) this median tract has risen in front of the great fon- 

 tanelle (Jo.) as a rudimentary "mesethmoid" (p.e.). 



The fontaneUe (fo.) is large and elegantly lanceolate; the walls are well developed, 

 and the roof (tr.) exists as a marginal band from the hinder complete roof (above nc.) 

 to the up-growing middle wall ( j->.e.). 



The wings of the ethmoid (each side of 2^-<?.) are very indeterminate at present, and 

 there is no distinct elevation outside them forming a rudimentary post-palatine. The 

 inner nostrils (i.n.) are wide ajjart — unusually so — and small; in front of them the 

 trabecular are lobate to catch the pre-uarial ligament, wliich arises from the blunt pre- 

 palatine spm- (mside (j.). The cornua (c.tr.) are very long, narrow, and sinuous ; they 

 each send out a sharp external angle. The suspensoria have a thick jiedicle (fig. 9,pd.), 

 a thick curved otic process (fig. 8, ot.j).) and a short and broad orbitar process (ot-.p.). 



The ethmo-palatine band {p.py.) is wider than long, the suspensorium coming 

 very close to the trabecula ; beyond this band the quadrate region (7.) is one-third 

 wider than it is long, and the pre-palatine spur is very blunt. The mandibles [mk.) 

 are extremely large and massive ; the angular process is short and thick. The lower 



