DEVELOPMENT OF THE SKULL IX TUE BATJRACHIA. l59 



thx'e tracts of bone, as in tlie young- of Rana teiiqjOJXiria (Phil. Trans. 1871, Plate 8, 

 fig. 7, eth.). 



The broad end of tlie egg-shaped fontanelle (/o.) is bounded I)y a very narrow 

 tegminal tract ; this tract is ossified, at first, evidently, as in the young of Raiia 

 temporaria of the first autumn, by ossification of the fibrous investment, and then by 

 some degree of endosteal deposit. In Dactylelhra (Phil. Trans. 187G, Plate 59, fig. 1, 

 s.eth.) the ossified membranous tract is large and X'^haped, but it does not unite with 

 the extensively ossified chondrocranium ; but in the phaneroglossal Anura, any 

 external bone there ma}- be is soon lost in the deeper ossification. 



In this "dwarf" the superior marginal crescent of bone seems to have started in 

 growth from symmetrical points, but of this I am not certain ; it may have been single 

 and median at first, and then have become partly sub-divided afterwards — a very 

 common thing in this group. In this narrow ethmoidal girdle the " axils " ai-e 

 ossified {eth.), and their limited lateral tracts unite with the arch of bone above, 

 inside the superorbital band. That band {s.oh.) is double, there is a narrow tract 

 over the anterior angle of the orbital space, and a wider lobe projecting from the 

 ethmoidal wnng ; these two are separated by a deep rounded notch. 



The true nasal region is altogether unossified ; it is of a good size both in length 

 and breadth. The septum {s.n.) narrows a little, forwards, from the perpendicular 

 ethmoid, and ends in front in a shortish, rounded rostrum (figs. 6, 7, 9) ; this 

 rostrmn is margined by the nasal roofs, and the front of this region is sinuous, 

 and retires considerably, right and left. The pro-rhinals (figs. 7 and 9, li.rh.) are 

 smallish and falcate. The broad subnasal laminae (fig. 7, on each side of s.n.) grow 

 out into ear-shaped angular processes. The extei'ual nostrils {e.n.) are as wide apart 

 as ill other " Polypedatidse ;" they are almost as far ajmrt as the mner openings 

 {i.n.); the valvular cartilages [u.l^.u.l-.) are normal. 



The palato-suspensorial arches are normal, but feeble, so also are the bony tracts 

 apphed to them {pa., pg.); both the hinder forks {pel., q.c.) are short, and the quad- 

 rate is not ossrfied. 



The Eustachian openings {eu.) are nearly circular: they are two-tlikds the size of 

 the inner nostrils; the annulus (figs. G, 10, a.tij.) is rather small, and imperfect above. 



The mandible (not figured) is normal, but feeble; the stapes (tig. 10, st.) is nearly 

 semicircular, and has a long " boss ;" the mtei"-sta2)edial is not cut ofi:" from the dilated 

 and forked end oi' the stout arcuate medio-stapedial {m.st.), but is a massive, emar- 

 ginate lobe of cartilage. The extra-stapedial {e.st.) is the short unossified end of 

 this non-segmented columella ; it is an inverted saddle-shaped process, and has no 

 ascending ray. This small " key ' is embedded in a thick cushion of fibrous and 

 fatty tissue. The stylo-hyal end of the rest of the hyoid arch is not coalesced 

 above ; the descending bar (fig. 8, c.hy.) is of the normal width for the greater part 

 of its length, but widens before it turns back into the hypo-hyal region {h.Juj.); this 

 part has no front lobe, but on its outer side there is a small oval " extra-hyal " 



