DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 137 



Tlie prootics and ex-occipitals (e.o. to V.) are one undivided mass of bone, i-ight and 

 left, and the tracts are margined by cartilage, outside and in. 



The outer tract, above, is the widish oblong tegmen tympani (t.ty.), beyond the 

 horizontal canal (h.s.c.) ; below, the vestibular region [vh.) is largely unossified. 



In front, the bone reaches to the foramen ovale (V.). Thence the cranial trough is 

 unossified for three-fifths of the region of the orbits ; in the hinder half of this tract 

 the optic fenestra {o.s., II.) is very large. 



The girdle-bone (eth.) does not ossify all the ethmoidal region in front ; it reaches 

 farther below than above, and thei-e it projects somewhat into the "wings," and 

 i-eaches forwards most in the middle. 



The fore part of the great, single, open fontanelle (/o.) cuts away a semi-circle from 

 the girdle-bone ; three-fourths of it is uncovered by the arrested roof-bones. The fore 

 ]iart of the ethmoid and all the nasal territory is unossified; the septum nasi (,s-.?i.) is 

 large and clearly marked, and the subnasal laminae (fig. 2, s.n.I.) are very large, even 

 at their narrowest part, mesiad of the internal nostrils (*.??.); their notched outer 

 edges neaidy reach these passages. The " intertrabecula " only forms as a knob in the 

 prenasal region ; the angles of the subnasal laminae are triangular, and spread into 

 the maxillaries at their fore end. 



The secondary cornua, or pro-rhinals (p.rh.), are long, slender, and out-tnrned. 



The nasal roof-cartilages form a mere rim to the septum nasi (fig. 1, al.n., sji.), but 

 they swell out into a curious bag of cartilage in front. This bag lies on the fore part 

 of the subnasal lamina, and is confluent with it ; the premaxillary encloses part of 

 this bag, as well as the pro-rhinal band. 



The thick upper and fore part of the nasal roof stops abruptly, the cartilage dipping 

 down in front ; after forming the bag, it grows up again, behind the large outer nostrd 

 (e.n.), which is protected, in front, by the three-toothed outer and upper labial {u.P.) ; 

 this is attached to the inner labial {u.lK), a large oval segment, inside the nasal process 

 of the pre-maxillary. 



These nasal pouches look like those of Dactylethra, but in that type these bagpipe- 

 shaped pouches are formed out of the large upper labial ; the true nasal roof being 

 a small band over the nasal sac, on each side (see Phil. Trans. 1876, Plate 59, figs. 1, 

 3, 5, and 6, u.l.). 



The ethmo-palatines {e.-pa.) are wide, diverging, cultrate bands, emarginate in front, 

 with a wide pre-palatine blade (jjr.pa.), and liaving the post-palatine bar {pt.pa.) 

 continuous with the pterygoid as one arcuate cartilage, but little affected behind by 

 the normal pterygoid bone (^sgr.). There is no palatine bone, but the pterygoid runs 

 far forwards ; behind, it bifurcates as usual, to invest the large pedate pedicle (pd.), 

 and to clamp the inside of the quadrate stem (fig. 2, sjx) This region is only a little 

 affected by the quadrato-jugal (i/.j.) ; its condyle (q.c.) is small, but normal ; it reaches 

 only a little behind the very small Eustachian pouch (eii.). 



There is neither annulus tympanicus, or columella ; the stapes (figs. 1 and 4, st.) is 



MDCCCLXXXI. T 



