46 MR. "W. K. TARKER ON THE STRUCTURE AND 



this is greatly in contrast with what is seen in 7?. pygmaa, for it has, like many other 

 small Batrachians, very little condyles, very wide apart. 



The lower face of the occipito-auditory mass runs across at exactly a right angle to 

 the axis of the skull, but when its whole extent is seen from above its outer angles 



to 



are seen to be bent forwards. '"' 



This lower face, from one "stylo-hyal" to the other, is a broad tract, one-third 

 longer and one-third broader than the straight and almost evenly oblong interorbital 

 region. The prootics and ex-occipitals {pr.o., e.o.) of the same side are confluent, but 

 there is a distinct synchondrosis both above and below (figs. 1, 2). A slight edo-e of 

 cartilage remains to the floor of the tympanum, and a larger tract to its "tegmen" 

 (fig. 3) ; nevertheless the ossification is intense, and readies in front within a short 

 distance of the optic foramen (II.). Also the girdle-bone is more than twice as 

 extensive as in the medium type ; it abuts upon the optic passage behind, and besides 

 tlie whole ethmoid, with its outer wings, runs half way along the proper nasal roof, 

 floor, and middle wall (figs. 1, 2, and 3). 



A small superorbital projection can be seen over the inner canthus ; these, and the 

 wings of the ethmoid, up to the point where segmentation takes place in Bufo, are 

 ossified. 



As to the fore and middle parts of the endocranium, we see some curious results 

 of overgrowth. First, the cranial " barge" appears to be very small and contracted as 

 compared with the huge arches of the facial outworks ; and, in tlie second place, the 

 nasal labyrinth is greatly exposed by the retirement from it of the facial aiches, in 

 their wide sweep outwards. In the smaller kinds (see Plate 6, fig.s. 6 and 7) the nasal 

 labyrinth is cai'ef'ully packed between the lamin;B of the premaxillaries and maxillaries. 



In the upper view (fig. 1) we see the nose lying naked, for the most part, between 

 the bony boundaries; the oiiter angles of the floor {ctr.) lying on the palatine lamina 

 of the maxillaries, but not hidden by the upper plate. The ascending part of the 

 outer angle of the floor (fig. 3, n.w.) is considerably ossified ; it reaches the roof (al.n.) 

 above, and coalesces with it. There is a " j^i-enasal rostrum" (in front of «.?;.) of 

 moderate size, and large subretral pro-rhinals (p.rJi.) ; the labials (ii.P., ii.l'~.) also are 

 well developed round the circular aperture (eji.). 



The cartilaginous palato- quadrate arch, on each side, is almost eaten away by the 

 ectosteal palatine and pterygoid (^a., pg-), the one thick and spatvdate, the other a 

 strong triradiate bone.t 



* In the lower view (fig. 2) I liave only figured tbe parts that come immecliately iinfler notice ; the 

 distant upper parts are left out, as they are not necessarily seen by the eye when discriniiuuting the lower 

 surface. The upper view must be compared with this to get a complete idea of the form. 



t In this and in a large number of Batrachia these two bones are as truly ectosteal as the sheaths of the 

 columella or of the thyro-hyal, and berome truly homologous with the perichondria! laminaj of the prootic 

 oxoccipitals and sphcnethmoid. I therefore colour them, throughout, as endoskeletal bones. In the 

 " Shoulder- girdle" we see the same temporary distinctness of the perichondrial, from the endosteal tracts of 

 bone, in the " pro-coracoid " and " .siipra-scapula." (See my " Shoulder-girdle and Sternum," Plates 5-7.) 



