DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 229 



make it normal ; it is large, weU developed, and has a spatulate extra- and a ligulate, 

 fixed, supx-a-stapedial {est., s.st.). 



The stylo-hyal (st.h.) is confluent ; it is not enlarged above, as in tlie other kind ; 

 the rest of the bar (fig. 4, c.Iu/., Ii.hi/.) is narrow, without a lobe. 



The lateral lobes of the basal plate {b.h.br.) are well developed, the notch in front 

 and the main plate are of the average size, and the thyro-hyals (t.hy.) are long, and 

 moderately divergent. Between them there is a thick, ossified mass, with a free 

 rounded fore margin ; tliis is the last basi-branchial {b.br.) ; its hinder margin is grooved. 

 In front of this bony ridge the plate is keeled, below, and this keel expands behind 

 the front notch iiito a triangular mass, the first basi-branchial ; the whole keel is more 

 or less calcified. 



The three cbaracteristic hyo-branchial plates of this and the two other kinds 

 (Plate 43, figs. 4, 6, and 10, — Engystoma) evidently belong to three closely related 

 species. 



In the main skull (Plate 43, figs. 1, 2) the investing bones are as feeble as the 

 centres in the chondrocranium. The fronto-parietals (fig. \,f.p.), thin shells pointed 

 in front, dilated postero-externally, and nowhere meeting at the mid-liiie, exactly 

 correspond to their counterparts in metamorphosing Common Tadpoles. So also 

 the broadly-crescentic nasals (h.) with their facial handle, and the frail marginal 

 bones {px., mx., q.j.), and. running along the suspensorium, the squamosal («'/.). The 

 parasphenoid (fig. 2, pa.s.) has its basi-temporal wings larger than it cochleariform 

 rostrum ; the hind part is a large triangle. 



The small ragged vomers {i\) have all the four normal processes, in size and develop- 

 ment they come between those of this and the next kind ; they protect the inner edge 

 of the rather small, round, inner nostrils [i.n.), which like the outer (e.».) are extremely 

 wide apart. 



In some things this skull comes nearer the " norma " than the two last, viz. : in its 

 perfect anuulus, well-developed columella, and distinct prootics and ex-occi]iitals. It 

 is farther from it in the extreme feebleness of all the bony tracts in the mam skull, 

 and in the total absence of the girdle-bone ; also in the retention of the " orbitar 

 process;" the clear regional mark between the post-palatine and pterygoid cartilaginous 

 tract ; in the more perfect development of the thick, bony, uncinate last basi-branchial ; 

 and especially in having a rudiment of both a supra- and a basioccipital. 



These minute forms are weU worthy of study in their irregular, and as it were, 

 halting metamorphosis ; and this is to be noted, namely, that generic groups may be 

 made according to the taste of each individual Zoologist ; no two species agree in all 

 things, and in some existing genera each species might be put by itself, and have its 

 own generic, as well as specijic, name. 



