DEVELOPMENT OF THE SKULL IN THK liATRACHTA. G3 



The hinder bony centres {e.o., pr.o.) are just such as would be found in a Common 

 Frog two-thirds grown ; now, a considerable amount of roof, floor, and periotic capsules 

 are soft. So also the "girdle-bone " (eth.) is not of gi-eat extent, it liardly reaches half 

 •way to the large optic fenestra (II.) ; from this space to the foramen ovale (V.) the wall 

 is also unossified. The palatu-suspensorial arch, and its ectosteal plates (pa., pg.), 

 are quite normal ; the condyles of the quadrate are very large, and the cartilage at 

 that part is but little affected by the quadrato-jugals {q.j.). The pedicles are wide 

 apart, and well developed ; the Eustachian passages (e».) are large and oblique. 

 The annulus {(t.tij.) is moderate and complete. The stapes (Plate 14, fig. 10, st.) is 

 large, thick, and oval ; the medio-stapedial (m.^f.) fits inside it by a decurved unossified 

 lobe ; but the inter-stapediul is not distinct. The medio-stapedial is therefore large 

 beliind ; it is straight, and joins on to the narrow stalk of a broadly spatulate extra- 

 stapedial {e.st.), which becomes double on its inner face, giving off a strong ligulate 

 supra-stapedial (s.st.) which is confluent with the "tegmen" above. The stylohyal 

 part of the hyoid band {fit.h.) articulates with the floor of the tympanium, and turning 

 round, borders the Eustachian opening (eu.). 



The investing bones, one and all, are extremely like those of the type ; there is a 

 septo-maxillary on each side, but it is small. 



The mandil^le shows in the dentary (fig. 7, (/.) very little of the crest ; yet in 

 old individuals the mandible is high at that part, and also somewhat hooked at the 

 synchondrosis, like an old male Salmon. 



The hyo-brancliial plate (fig. 8) is normal, but its lateral lobes are badly developed. 



15 (continued). — (B) Tomopterna hreviccps. — Adult female, 2 inches long. Ceylon. 



The distinction between the skull of the half-grown young of this species and the 

 young of a Common Frog of the same age, is slight as compared with what is seen in 

 their adult condition (Plate 15, figs. 1-4; and Phil. Trans., 1871, Plate 9). 



The facial outline now forms half a rather short ellipse, and the greatest breadth is 

 nearly one-fourth more than the length ; moreover, this is one of the highest (or 

 deepest) of the skulls in the whole Order. 



Indeed, this Frog is an isomorjjh in respect of its short deep head and its thorough 

 want of neck of the most remarkable Toads of the .same (the Oriental) territory, e.g., 

 Callula, Diplopelma, Cacopus. 



This, again, is an instance of what is seen in the main geographical territories, viz. : 

 that some particular modification characterises the members of very ditlerent "Families" 

 of the same Order, as if the Anurous type had, in each territory, broken up into 

 groups isomorphic of, but not immediately related (geneticalli/) to, those of other terri- 

 tories. Thus from a generalised root-form, in territories wide apart, there may have 

 sprung, in each place, independently. Frogs with teeth and Tomfs without teeth ; 



