66 Zoolocjical Society : — 



is very small and narrow, and accessible only to a thin bristle ; tlie 

 tube passes near the united os sphenoideum and petrosum inwards 

 and towards the back, crossing the carotis and the ner\u3 vagus. 

 The membrane by which it is formed becomes gradually excess- 

 ively thin, and is closed without an aperture near the fenestra 

 ovalis vestibuli. This aperture is really oval, closed by a cartilagi- 

 nous cover and in direct contact with muscles ; the nature of the 

 vestibulum is proved by the soft white calcareous concrement. Such 

 I found to be the structure of ear in Hemisns cjuttatus and Mi- 

 crhyla. In Phryniscus Icevis and nigricans and in Brachycephalus 

 the osteum pharyngeum of the tube is more open. Rhraophrynus 

 dorsalis exhibits'the following details : — After removing the skin, an 

 aperture of the ear is no more observable than a tympanum exter- 

 nally, the whole region being covered with muscles. The most accu- 

 rate and repeated examination of old and young individuals did not 

 enable me to find any osteum pharyngeum of the tube ; at the point 

 where it might be supposed to be situated, on the sides of the pala- 

 tum molle, I found only a very short and flat groove, perhaps the 

 same seen by Bibron, who describes the eustachian tubes as ex- 

 cessively small. After removing the muscles, the external entrance 

 in the ear becomes conspicuous ; it is the fenestra ovalis vestibuli — a 

 large opening with a rounded outline, formed by swollen edges of the 

 OS petrosum. This opening is closed by a cartilaginous operculum, 

 internally concave, externally convex, and so inserted by a membrane 

 in the bony ring as to be rendered moveable. Round the bony ring 

 arise some muscular fibres, which continue to the front edge of the 

 shoulder-blade. Other muscular fibres, having arisen from the centre 

 of the operculum, join them ; and their function is, by moving the 

 operculum outwards, to enlarge the cavity of the vestibulum. The 

 vestibulum itself is spacious, quite bony, and forming an externally 

 conspicuous, thin, flat bulla. In the interior is enclosed in the 

 saccum vestibuli — a large, rounded, white and soft calcareous concre- 

 ment. Besides the fenestra ovalis are to be observed 3 or 4 minute 

 openings, through which a bristle can reach immediately the cavity 

 of the skull, and a larger one, oval, near the canales scmicirculares. 



Thvis we find in these Anura slight modifications in the type of the 

 structure of the ear, as it is found in the CceciHcB and Urodelce (Am- 

 2ihiutna, Menoj^oma, Sireclon, Proteus, Triton, Salamandra), — a cir- 

 cumstance which directs us not to neglect it as a character for 

 systematical arrangement ; and therefore I divide the Opisthor/lossa 

 oxydactyla vca^ jilatydactyla into the following sections : — 



I. Opisthoylossa oxydactyla. 



1. With maxillary teeth and perfectly-developed ear : Ra^iina. 



2. AVith maxillary teeth and imperfectly-developed ear : Bom- 



binatorina. 



3. Without maxillary teeth, and with imperfectly-developed 



ear : Brachycephalina. 



4. "Without maxillary teeth, and with perfectly-developed ear : 



Bi(fonina. 



I 



