DEVELOPMENT OF THE SKULL IN THE 13ATRACH1A. Ill 



This larval skull will be best described by comj^aring it with the next (Plate 22, 

 figs. 6-9 with figs. 2-5) ; all these objects are shown as mngnified five diameters ; the 

 Tadpole of Cahjptocephalus was fully one-third larger than that of Cyclorhamphus, and 

 in the latter the hind legs were four times {relatively) as long as in the former, and 

 therefore it must have been somewhat more advanced in development, generally. 



Indeed, this will be seen by comparison of the figures ; yet tliis is too slight to 

 effect the general form and relations of the parts. 



The interauditory region, in this, is altogether narrower ; the interorbital much 

 more uniform, not narrowing, forwards, lialf as much ; and the palato-suspensorial bars 

 converge more. On the whole, however, these two skulls might easily be taken for 

 those of two species of tlie same genus ; part fur part, and process fur process, there 

 is a very close resemblance between the two. 



The notochord [iic.) is still found between the halves of the basal plate ; the 

 occipital condyles {oc.c.) have the same form ; the ex-occipitals (e.o.) are more deve- 

 loped, answering to the longer legs, and are seen beyond the twin nerve-passages 

 (IX., X.). The hinder "tegmen" only runs half as far forwards, and is not fenestrate, 

 whilst the fore "tegmen" is finished and the single fontanelle {fo.) is a large evenly 

 oval space, instead of being a smaller space, shaped like an oval leaf, with the stalk 

 in front. The auditory capsules are not thrust so far out ; they are naked, and show 

 the canals [a.s.c, h.sx.j'p.s.c.) through then- diaphanous walls ; the spurs growing from 

 the " tegmen tympani" are very similar (t.tij.'^, sp.c.) ; the stapes (st.) is like that of the 

 next. 



The almost oblong interorbital region (fig. 7) is shorter, and scarcely bulges at 

 all ; its walls are perfect and run an edge over the roof, on which the bony " wall 

 plates " lie. The front tegmen runs forward as a wedge-like mass, for it has coalesced 

 with the more developed iutertrabecular crest, and the " lamma perpendicularis " {p.e.) 

 is now formed. The lateral ethmoidal wings (al.e.), and the upgrowths of the tra- 

 beculte, outside the emerging olfactory nerves (I.), have conspired with the median 

 crest and the roof to finish the plaster model for the future " girdle-bone." The first 

 rudiment of the septum nasi exists, now, mei'ely as the foremost part of the inter- 

 trabecula ; beyond this frail commissure of the paired bands the cornua trabeculaj 

 (c.t):) diverge, arching both outwards and downwards ; they are longer and narrower, 

 and more diverged than in the next, making the lozenge-shaped interspace left by 

 them and the upper labials {u.V'.u.V'.) mucli wider. 



The palato-suspensorial arch {pd., i^.pj., ip) shows its likeness and its unlikeness 

 to that of the other species. The pedicle {pd.) is longer and the otic process is not 

 distinct from the rounded " elbow " of the cartilage, which is bent backwards more. 

 This, with the gradual convergence of the main bars, makes the orbital space wider 

 behind ; it is, also, shorter. The orbitar processes {or.p.) do not overlap so much as iu 

 the next, but keep outside the post-palatine rudiment (pt.pa.) ; this crest fails iu its 



• Iu fig. G this is wrongly lettered f.cr. 



