DEVELOPMENT OF TTTE SKULTv TN THE BATRACHTA. •'>•'' 



seen in tlie skull of small kinds, and bringing into prominence parts that also project 

 largely in osseous Fishes. Tiie epiotic region burrowed by the posterior canal (cp.) 

 stands out, divergingly, on each side of the great archway, with its transversely oval 

 entrance (fig. 4). The anterior canal sweeps round the front ; outside it there is 

 a great hollow, and then the periotic mass rises over the horizontal canal, this it 

 does still more at the edge (teg men tijmpnni). The outer margin grows backwards 

 into a large terete imosslfied " pterotic" ridge {pt.o.) — the part that is ossified by the 

 ])terotic hone in Teleostei. The whole structure is, on the whole, bony up to the fore 

 margin of the foramen ovale, and these right and left masses are confluent over the 

 foramen magnum, but not below (fig. 2) ; there is a small tract of cartilage in the 

 basioccipital region. 



Below, the twin po.st-aural nerve passages (fig. 2, IX., X.) are wide apart, and the 

 antero-external margin of the ear-capsule is bevelled away and covered with a plate 

 of cartilage for articulation with the pedicle (pd.). The ear-masses and intervening 

 hind skull together make only a third of the whole width at this part ; above 

 (fig. l) the pterotic crests (j^f-o.) stand further out, where they pass beneath the 

 squamosal (sq.). 



Suddenly in the temporal region the skull is compressed to two-thirds its average 

 Avidth, then becomes of a fuller form, and gently narrows again before it spreads out 

 into the wings of the ethmoid, opposite the closing in of the cranial trough. 



The optic fenestra (II.) is moderate ; it is margined by cartilage in front, above, and 

 below, and the girdle-bone (eth.) has not much more interorbital space than this tract, 

 which lies in front obUquely over the bone. There is a small ossified superorbital lobe 

 (s.oh.). The cruciform bony mass only reaches in front to the proper morphological 

 edo-e of the ethmoidal territory ; all the true nasal region is unossified. The whole 

 nasal roof is a winged sub-pentagonal tract, not ending in more than a bud of the 

 " prenasal," and with half its septal part and a headland of its roof uncovered by the 

 nasals (fig. 1, s.n., n.r., n.). The outer nostrils (figs. 1, 3, e.n.) are protected by the 

 usual inner and outer upper labials {u.P.n.I-.). The roof runs forward, narrowing; the 

 floor (fig. 2, s.n.) is sub-quadrate, and is finished antero-externally by the curious 

 cenacorn angles (Plate 8, fig. 2, and Plate 9, fig. 7, s.n.L). The septum (s.n.) below is 

 very thick in front, and narrows backwards towards the ethmoid bone ; the angles of 

 the subnasal lamina behind pass into the large, widely-extended ethmo-palatines which 

 are curiously covered with splints, above and below. 



On each side of the bud-shaped end of the septum there is a rather large fenestra 

 (Plate 9, fig. 7, s.n.), and in this enlarged figui-e of part of this region we see the pro- 

 rhinal {prh.) ; it is very large, sub-flabelliform, and turned (contrary to rule) inwards. 

 In this same figure the angle of the nasal capsule, a part derived from the trabeculie, 

 is seen to give off a curious retral proce.ss (al.n., s.n.l.) : this is quite normal. 



The whole palato-quadrate arch {pa., pg.) is an immense structure; measured from 

 the pre-palatine spike to the end of the condyle, it equals the entire length of the 



