2 8 ANURA CHAP. 



The Anura possesses five well-developed toes with normally 

 2, 2, 3, 4, and 3 phalanges, and the rudiments of a sixth digit, 

 the so-called prehallux, which consists of from two to four 

 pieces, including the one which represents its metatarsal. This 

 prehallux, as a vestige of a once better developed digit, is 

 exactly like the elements on the radial side of the wrist, which, 

 we are certain, are the remnants of a once complete finger, namely 

 the pollex. The only weighty difficulty against its interpreta- 

 tion as a prehallux lies in the fact that hitherto no six-toed 

 Stegocephali have been found ; but the fact that there are no 

 Stegocephali known with more than four fingers could be used as 

 an argument against there being a pollex -vestige in recent 

 Anura with just as little reason. 



The skull of the Anura differs from that of the other recent 

 Amphibia in the following features : — 



The orbital region of the primitive cranium remains carti- 

 laginous, but further forward the cranial cavity is closed by the 

 unpaired sphenethmoid, which forms a ring round the anterior 

 portion of the brain -cavity, hence called " os en ceinture " by 

 some anatomists. The frontals and parietals fuse into one pair 

 of fronto-parietal bones, and these again can fuse together in the 

 middle line ; as in Aglossa and Fe/ohcUes. The palatal portion of 

 the palato-quadrate cartilage is complete, reaching forwards to the 

 sides of the ethmoid region. The curved arch, formed by this 

 cartilage, is covered by the following bones: (1) the quadrato- 

 jugal, reduced to a thin splint which connects the quadrate and 

 squamosal with the posterior end of the maxilla; (2) the ptery- 

 goid, always strong, extending from the distal inner corner of 

 the quadrate to the maxilla, sometimes also to the palatine, and 

 with a broad, median process to the parasphenoid, this process 

 covering ventrally most of the otic region ; (3) the palatines, 

 which vary considerably in shape and size ; they are placed 

 transversely and meet in the middle line: in Bomhinator and 

 Pelodytes they are absent. 



The quadrates are directed transversely and backwards, in 

 conformity with the wide gape of the mouth. The squamosal is 

 always well developed, covering the whole of the quadrate on its 

 outer side ; it has a forwardly directed process which ends freely 

 in Rana, meets a corresponding process of the maxilla and forms 

 a bony arcl) with it in Discoglossns, Pelohatcs, and others, or 



