DEVELOPMENT OP THE SKULL IN THE BATRACHIA. 129 



Directly in front of these ethmoidal crests the trabeculae are at their narrowest, are 

 closest together, their scooped edge forming the inner margin to the internal nostrils 

 (i.ii.) ; the complete hind viia is formed bj^ the crescentic fore edge of the pterygo- 

 palatine band {p.pg.). In front, the quadrate part of the suspensoriura {q.) and the 

 trabeculfe {ctr.) of the same side each send out a bud (pr.pa.), and these approaching 

 growtlis are united by a fibrous band which finishes the nasal opening. The cornua 

 trabecula; maintain their average width up to the frontal wall, but are narrower and 

 are longer than usual, diverge very gently, and end in a moderately pedate process, 

 which is turned outwards. 



The nasal roofs are not yet chondrified, the eyeballs have been removed with the 

 other soft structures, but the auditory capsules are shown, for they are built into the 

 walls of the cranium as side chambers. Below (fig. 2), there is no columella at present, 

 but there is an open space, and into this space — the fenestra ovalis — the oval " stapes " 

 (fig. 'Z, vh., St.) fits. 



The roof of the future tympanic chamber {t.t;j.) is very largely developed; outside 

 the large horizontal canal {h.s.c.) it sends out a small hinder, and a large front, spur ; 

 the latter is the confluent "spiracular cartilage " (sjf.c.) — the " annulus " that is to be; it 

 just touches and overlaps the otic process (a free elbow now) of the suspensorium (ot.p.). 



The anterior canal {a.s.c.) is covered with bone {f.p.), the posterior (p.s.c.) is naked, 

 and bulges gently above and behind. A small circular plate of bone, the ex-occipital 

 (e.o.), has grown inside the double nerve-passage (IX., X.) and encloses and subdivides 

 it externally. 



The roof is covered to a great extent by the fronto-parietals {f.p.) ; these are many 

 times larger than those of any other larva at this stage dissected by me (see Plates 

 2, 3, 4 ; also Plate 22, figs. G, 7). 



The two bones are very granular and rugose, quite unlike what is seen in the other 

 Tadpoles, they, together, have an emarginate bow-shaped hind edge spread over the 

 large ear-capsides up to the horizontal canal (h.s.c), which they partly cover, and then 

 occupy two-thirds of the interorbital region of the roof. Each bone is deeply notched 

 on the inside, half-way ; this is the beginning of the segmentation into two bones ; the 

 space thus left bare is roofed by the front part of the liinder tegmen. Behmd the 

 notch the bones come closer together, ready to form a sagittal suture, in front they 

 diverge to their pointed end and have a rounded inner edge. 



But the parasphenoid (fig. 3, pa.s.) is also rugose, pitted, and shows signs of a "ganoid " 

 nature ; this is lost in the adult, as if the larva retained more of the nature of some 

 ancient armed type than the adult. The bone is similar in form to that of Cydorhamphus 

 (fig. 7), and not much larger, relatively ; it is very lax'ge in both kinds ; it is broader 

 altogether, and notched at the tip ; and the basi-teniporal wings are, like the tip, 

 less acuminate than in the other Tadpole (fig. 7). 



This condition of the roof and floor-bones in a larval Batrachian just putting forth its 

 hind legs is of extreme interest ; and the size, uiassiveness, and sculpturing of these 



MDCCCLXXXI. s 



