t)EVKLOPMfiNT OF THE SKULL IN THE BATRACHIA. 207 



as the one next to be described, viz.: the Tadpole of B. lentiginosus, whose legs were 

 only a line long, and in which (see Plate 38, figs. 9, 10) the parasphenoid was 

 beginning. There is a remarkable want of uniformity in the time as to which certain 

 parts appear. 



From the root of the pedicle (pd) to the quadrate condyle (q.) we have the 

 generalised counterpart of the quadrate of the Sauropsida ; the metapteiygoid and 

 quadrate regions (together) of the Osseous Fishes. 



The free mandible (mk.) is only a short, thick, ray, with a notched condyloid tract, 

 like that of the " ulna," ending in an angular process, like the " olecranon." 



Another, much larger, cartilage is articulated to the side plate by a rovuided 

 condyle ; the hollow for it is under the orbitar process {or.p., hy.f.) : this is the stylo- 

 cerato-hyal [cjiy.), it is a flat phalangiform piece, enlarged both proximally and 

 distally.. and united to its fellow by simide cartilage. 



The succeeding ai'ches (branchial) have all been removed, and will not be described. 

 Over the curling, pointed, horns of the trabeculse there is a pair of semi-lunar 

 cartilages — notched beliind ; these are the upper labials {u.l.) not divided into two 

 pairs. 



Below, between the mandibles, there is another pair (/./.), arranged crescentically ; 

 they unite with each other in the middle, and are scooped, above. 



Above, and below, these labials are covered with the serrated horny plates that form 

 the primary dental apparatus or " odontophore " of the Tadpole, whicli vanishes away, 

 or is moulted off, during metamorphosis. 



This skull is unlike enough to that of the adult Toad, and would be even if no 

 investing bones appeared, nor any bony tracts in the endocranium ; the passage of 

 the larval into the pennanent skull has, however, in this group, already been 

 described. I shall now compare this and the next together. 



59. (A) Tsid^ole oi Bufo lentiginosus. — finch long; hind legs, -i-o inch long. Penekese 

 Island, Mass., U.S. 



The skull of this Tadpole (Plate 38, figs. 9, 10) (which was the same length as 

 the last) is nearly a third longer, but very little wider ; its breadth is only three- 

 fourths of its length, and not nearly equal to it, as in the last kind. 



The difference between this skull and the last, and of both of them from that of 

 B. vulgaris, is very remai'kable, showing that the variations in the adult do not arise 

 out of a uniform larval " model ;" the species, even, begin to vary as soon as they are 

 hatched. 



In this specimen the hind legs are apparent, the Tadpole is only f of an inch long, 

 and both this and the last are smaller larvae than those of the Common Toad. 



In Pseudis (A), as we have seen, the legs have relatively less development, but the 

 skull is largely ossified, and as large as a crown-piece, the whole length of the Tadpole 

 being 10^ inches, and its tail 4 inches across (Plate 1, fig. 1). Here, the skull is 



