DEVELOPMENT OF THE SKULL IN" THE BATRACHIA. 99 



5. The palatine ectostoses are in two pieces on eacli side. 



6. The quadrate is partly ossified, 



7. There is no distinct inter-stapedial. 



8. The supra-stapedial is confluent, above. 



Fittli genus. Lymnodijiiastes. 



23. Lymnodynastes tasmaniensis. — Adult female ; If inch long. Tasmania. 



This is a long skull (Plate 18, figs. 5-8), with short auditory, long nasal, and 

 average orbital, regions. The length is the fortieth of an inch greater than the 

 breadth, and the outline of the face is half a lone; oval. The sides are rather straiofht 

 in the jugal region, for the broad and long nasal region makes the fore edge a regular 

 semicii-cle. The whole ethmo-nasal territory is, as compared to the skull cavity, as 

 2 to 3 in length ; the average fore and aft extent of that territory, as compared 

 with that of the cranium proper, is as 1 to 2. The occipital condyles (oc.c.) are of 

 moderate size, and of the usual distance from each other ; they project but little, are 

 more jiosterior than inferior, and the emargination of both floor and roof is crescentic. 



The auditory capsules are of moderate size and become narrow at the tegmen (t.ty.); 

 the cranial interspace between them is very wide, especially in front. 



The ethmoidal region {eth.) is also wide, and the broad flat skull is almost like au 

 hourglass, being much the smallest in the middle, and thus the suborbital fenestras 

 are almost oval in shape, the arcuate palato-jitery golds bounding them externally. The 

 whole pre-cranial region is very flat and outspread. 



The tegmen cranii (t.cr.) is more complete in this skull than in most of those known 

 to me ; it resembles in this respect the skull of the Skate, the roof growing along from 

 the sides, so as to leave, when the roof-bones are removed, a space little more than 

 a third as wide as the narrow interorbital region, and little more than a third the 

 length of the cranial cavity. 



Also those secondary spaces, so characteristic of the Anura, are absent, and the wide 

 inter-auditory space, above, is completely chondrlfied. The tract, moreover, in front of 

 the fontanelle (eth.) is large both ways, so that a very unusual amount of the girdle- 

 bone is exposed. The ex-occlpitals and prootics (e.o., pr.o.) are confluent for some 

 extent at their inner edge, above ; below, there is a good space of cartilage dividing 

 them. Above (fig. 5), the whole tegmen tympani (t.ty.) is soft, and a wedge-shaped 

 tract of cartilage is seen between the bones. Behind this ti-act the ex-occipital is seen to 

 reach outwards beyond the horizontal canal (h.s.c.) and Inwards to such a distance from 

 the middle that the superocclpltal region (fig. 5) is left of unnsual width. Below, the 

 basioccipital synchondrosis (fig. G) is only half that wldtli, and is quite normal. 



The prootics run forwards, above (fig. 5, pr.o.), over the optic passage, and inwards 



o 2 



