DEVELOPMENT OE THE STCITLL TN THE BATRACTTIA. 258 



are the auditory capsules ; large masses of cells, the rudiments of the ganglia of the 

 5th and 7th nerves, separate these globes from the pedicles of the suspensoria. 



The eye-balls are not taken into account ; the nasal sacs are entirely membranous, 

 at present. 



The parts displayed in the dissected head, and in sections through all the parts of 

 the head, lend colour to the suggestion that all the three j^airs of cartilages are 

 serially homologous : I believe this to be quite opposed to the true interpretation 

 of the parts ; that the inner bauds (trabeculge) are prematurely developed, paired, 

 axial parts, gi'owing beyond the notochoi'd, but paracJtordal in their hinder part : 

 moreover, in other types, as the " Urodeles " and " Marsipobranchs," the part embracing 

 the notochord is, from the first, much larger than in the " Anura." 



B. a. — Perfect clwndrocraninm : — before the formation of bony centres— in the 



" Phaneroglossa." 



The simple cartilaginous bars that were seen at first are soon developed into a 

 perfect chondrocranium of the Petromyzine type. 



The cranial notochord, besides its own mesoblastic sheath, whicli is now and then 

 chondrified even in the " Anura," becomes enclosed, right and left, between two solid 

 bars of cartilage — the extension, backwards, of the apices of the trabeculse (and not 

 as separate plates, as in the " Urodeles "); and these two basal plates are fused 

 together, for a short distance, in front of the notochord (see Phil. Trans., 1876, Plate 

 55, and the figures of larval skulls in the present paper). 



In the nasal region the trabeculae coalesce, and then send their elongated horns 

 forwards, and downwards ; in the interorbital region, each bar sends upwards a crest, 

 which becomes thick and bulbous near the coalesced part : here we have the beginning 

 of the cranial walls, and of the ethmoidal region, or closing-in part of the skull. 

 After a while, behind the ear-capsules, a wall, and then a roof, is formed — the occipital 

 arch. 



The large, bowed, twice-conjugated suspensoria develop a crest along theu- outer 

 edge, and this grows into a large leafy plate in the ethmoidal region — the " orbitar 

 process," which may (exceptionally), as in Bufo vuhjaris, coalesce with the ethmoid. 



The free mandibles grow larger, form a condyle and an "olecranon,"' and carry the 

 (suctorial) lower labials between them, as the cornua trabecula carry the upper or 

 overlapping labials. 



The third bar (liyoid — second visceral arch) grows more perfect in form, as well a.s 

 gets larger in size, but retiiins its primitive place under the antorbital region. 



The auditory (parachordal), orbital, and nasal regions are nearly equal in length, 

 and the auditory sacs become gradually completely invested with their own cartila- 

 ginous coat, which takes the form of the swelling and arching cavities within. 



