DEVELOPMENT OF THE SKULL IN THE BATRACHTA. 31 



occupied with a new (and rare) bony centre — the " pro-parasphenoid " {pa.s.) The 

 endosteal tracts in front of and behind the auditory capsules {pr.o., e.o.) are enlarging, 

 and the " pedicles " (pel.) in front of the former are becoming very attenuated. The 

 rest of the hind part of the cninium is but little altered, but in front the nasal capsule 

 is almost finished (fig. 4). 



The nasal roofs {al.n.) are now completely confluent with the septum and the lateral 

 wings of the ethmoid ; nevertheless the " cornua trabeculce " [c.tr.) that form the floor 

 of the nasal cavities are undivided in front. The ear-shaped nasal roofs are seen to 

 have curved down, round the external nostril (e.n.), but the terminal halves of the 

 trabecular cornua are interposed between the nasal capsules and the upper labials. 



These, however (figs. 4-G, u.J.), are seen to be breaking up into an inner and an 

 outer pair : these will disappear ; the new labials and the newly formed premaxillaries 

 have been removed. The inferior arches (Plate 3, figs. 5, 6, and Plate 9, fig. 1) are but 

 little altered fi-om what they were in the Second Stage. The drawing of the branchial 

 arches was made from an outspread preparation which was figured from below ; they 

 are seen to turn obliquely backwards as they ascend to the sides of the basis cranii. 



Tooth-like processes of simple cartilage are interdigated with each other in the large 

 clefts ; but the branchiae which grow on them, and which run inwards in rows, have 

 been removed. 



But truly cartilaginous rays grow from the bars under these processes ; these are 

 partly shown in Plate 9, fig. 3, hw. 



The internal nostril (Plate 3, fig. 5; Plate 9, fig. 2, in.) is a curious oblong slit, 

 diverging forwards, and protected by one or more papilhB. 



A series of transversely vertical sections (Plate 3, figs. 7-13 ; and Plate 9, figs. 

 4-6) show the soHdity of this chondrocranium. 



The l.s^ section (Plate 3, fig. 7) is through the fore part of the nasal capsule, and 

 catches the nasal roofs (al.sjo.) both above, and where they turn over to form the narial 

 rim, or " ahnasal " fold. Tliey have coalesced with the intertrabecular wall, now the 

 septum nasi (s.n.). 



A branch of the orbito-nasal nerve (5^) is seen emerging betw^een the folds ; the 

 cavity between these folds externally is the outer nostril ; another space is seen 

 below this and above the thick cornua trabeculse {c.tr.), which runs inwards to the 

 inner nostril. At present the trabecular horns are not modified into the flat nasal 

 floor, but are attached to the structure above by fibrous bands. 



The 2nd section (fig. 8) is close behind the nostril, and behind the second fold of 

 cartilage ; on one side the wide part of the roof has been (obliquely) cut through ; the 

 septum {s.n.) is still some distance from the cornua {dr.; the cross band is coloured, 

 by mistake). 



The 3rJ section (fig. 9) is similar ; it is also oblique, and the hinder part of the 

 capsule is partly severed. 



The 4th section (fig. 10) is through the widest part of the nasal roof, wliere these 



