Development of the skull in thk batrachia. 12/ 



than the main bar, and end by a ragged oblique edge, which runs to a point in front, 

 reaching nearly to the Eustachian opening (eu.). 



The middle of this hind part is raised into a lozenge-shaped convexity, but the main 

 bar, ■which is three-fifths the width of the trough of the cranium, is itself a deep 

 trough. 



Between the foramina ovalia (V. ) it is compressed a little, is widest between the optic 

 nerves (II), and then scarcely lessens to its rounded ragged fore end, where it reaches 

 the thick bosses of the vomer (v.) that carry the teeth. 



Those bones (fig. 2, v.) are very thick in their dentigerous portion, where they form a 

 lobe that runs outwards and a little forwai'ds ; the thinner part forms a strong spike in 

 front of the internal nostrils {i.u.), and a broad diverging lobe in front of the spike, 

 which reaches the maxillary imder the angle of the " subnasal lamina'' (s.u.l.). 



This cranial building is thus finished below and above ; its roof, floor, side-walls, 

 partitions, chambers, and outworks are all essentially such as we see, on a small scale, 

 in the Common Frog. But the great size of this skull, and the extension under the 

 skin of thick dense bone, ornate with, a honeycomb pattern of hollows and papidate 

 ridges passing into pearly grams, makes it in appearance very unhke its simple 

 "norma." These modifications may be classed under one head as modification No. 1. 



2. The upper fontanelle appeai-s to be single. 



3. The long inner process of the pterygoid aborts the Joint of the pedicle, 



4. There are distinct superorbital ledges. 



5. The quadi-ate is largely ossified by the quadrato-j ugal. 



6. There is no inter-stapedial segment. 



7. The extra-stapedial is suborbicuku', and its supra-stapedial process is confluent 

 above. 



8. The stylo-hyal is confluent above. 



9. The basal plate is very short, the hypo-hyals have no lobe, and the hind lobe is 

 very large and emarginate. 



These are the few, and for the most part gentle, differences between this skull and 

 that of the norma. 



30 (continued). — (B) C Gayi. — Larva; 4| inches long; tail, 2f inches ; hind legs, 

 ■J inch. Chili. 



In the large Tadpole of this species the chondrocranium (Plate 22, figs. 2-5) is 

 seen to differ in many points from that of the larvje of the American Bull-frogs 

 (Plates 3 and 4), and of Pseudis. 



It may be compared with the same (my first) stage in Kana pipiens (Plate 3, 

 figs. 1-3), Rana clamata (Plate 2, figs. 5-7), Pseudis paradoxa (Plate 2, figs. 1-4), and 

 with a somewhat more advanced stage of Cyclorhamphus cideus (Plate 22, figs. 6-9), 

 and with the larval skulls of Cystignathus, Hyla, Bufo, &c., iu other Plates. 



Its true relationship will be at once seen by a comparison of the figures on this 



