230 MR. W. K. I'ARKER ON THE STRUCTURE AND 



Thiid Family. " Brachycephalid^." 



Ear very imperfect ; no parotoids ; sacrum dilated. 



Genus Pseudopliryne. 



Q>7. Pseudophripie Bihronii. — Adult female, i inch long ; and adult male, f inch long. 

 New South Wales. 



The skull of this Bombinator Toad is another example of arrested metamorphosis 

 combined with ndapse, so to speak, into general vertebrate characters that are, 

 normally, suppressed in the Anura. 



Whether what we see in skulls like this is due to relapse, or the retention of more or 

 less unchanged, old, ichthyic, pro-Batrachian characters, the interest of the matter is 

 equal, for the transforming power which has wrought so mightily in the higher kinds 

 to set them on high above the fishy tribes, generally, has in these southern dwarfs 

 found some check, or has never, as yet, come into full play. 



The length and the breadth of this little skull are equal (Plate 42, figs. 1, 2), and 

 up to the hinges of the mandible the outline is a neat semi-ellipse ; but these hmges 

 are only opposite the scarcely open Eustachian cleft ieu.). Instead of getting some 

 distance behind the small occipital condyles, as in some types, the condyles of the 

 quadrate (f/.c) only reach along two-thirds of the length of the skull. The arrest, 

 generally, corresponds with what has been done in typical kinds by the time the tail 

 is well absorbed, or at most up to the first summer. 



The three regions of the skull are about equal in length, and the auditory capsules 

 are relatively very large, obliquely oval, with prominent canals {a.s.c, h.s.c, p.s.c.) ; 

 and the parotic outgrowth is nothing but the small unossified selvedge which forms the 

 tegmen {tt)/.). The occipital ring is very distinct and protrudmg, but the foramen 

 magnum (fig. 1) is very oblique, and open above. The ossification on each side is 

 generalised, for there is no distinction of prootic and ex-occipital (ow., vb., e.o.), and yet 

 it is very complete, except at the edge and the middle, above and below. There we 

 see the cartilage is wide and widening; above (fig. 1), it runs forwards to the fore-third 

 of the hind skull, and ends in a peak which converts the large, single fontanelle into 

 a heart-shaped space. 



Below (figs. 2 and VII., h.o., nc), the permanent cephalic notochord is covered 

 with bone (a " cephalostyle "), and this bony matter has run into the investing mass, 

 right and left, so that here we have a true, but arrested, " basi-occipital " bone. 



The broad, short mid skull lessens quickly up to the ethmoidal aire; it is rounded, 

 or swelling as in young Anura. The bone scarcely reaches the foramina ovaha (V.), 

 which are large, and two-thirds of the orbital wall remains unossified. Nearly half 

 that space is occupied by the large oval fenestra optica (II.), through the back part of 

 ■which the optic nerve escapes. At the fore edge of this space we have a bony tract 



