36 THE VOYAGE OF H.M.S. CHALLENGER. 



ends of the once free trabeculfe (tr.), has beguu to ensheath the intertrabecuk {i.tr.), 

 which is, manifestly, the prochordal homologue of the perichordal sheath, now hardened 

 into the " cephalostyle." The prepituitary part of the basisphenoidal region is marked 

 off from the presphenoidal region by a shallow notch directly in front of the pituitary 

 body {2yy.). 



At present, however, the hinder part of the existing wings of cartilage in the orbital 

 region (figs. 1, 2, o.s.) are due somewhat to incomplete absorption of the alisphenoids ; 

 they are -not quite reduced to their minimum development until after hatching ; they 

 always exist as a sharp edge to the auditory capsule in front. 



From the pituitary space to the frontal wall there is one large plate of unossified car- 

 tilage (fig. 1, p.s.,s.n.), formed originally from the upgrowing of the trabeculse and inter- 

 trabecula. This plate is thick below and subcarinate, the middle-piece dipping below the 

 side-pieces ; an oblique thickening divides the interorbital from the inter-nasal region, 

 and in front the septum nasi — formed in all but its hinder part of the middle cartilage — 

 sends downwards a short "prenasal" spike [p.n.). The orbito-sphenoidal wings [o.s.) are 

 very large, having as yet an alisplienoidal selvedge behind ; tKey form a trough in which 

 the "hemispheres" lie. In front of these "wings" the olfactory nerves (1) burrow 

 downwards into the nasal sacs, and these latter are covered over with the aliseptal 

 growths of cartilage (fig. 4, al.s}:)) ; in fig. 1 this roof is cut away in the part brought into 

 view. 



The ciuadrate {q.) is still quite unossified, and the epipterygoid (fig. 7, e.pg.) has not 

 been segmented from it, but lies as a sigmoid process of the pedicle {pd.) in a groove of 

 the pterygoid bone {pg.). The rest of the cartilage {q.) from where the base of the 

 pedicle ends, is arched, hollowed, and notched, a thick ridge margining the arched part 

 and running down the middle of the articular part on its outside. The condyle of the 

 articular part (fig. 3, q.c) is bilobate and transversely placed, the thick ridge on its outside 

 passing into the semicircular ridge for the attachment of the " cartilaginous annulus" (fig. 

 10) ; between its hind extremity and the articular part there is a large, rounded, inferior 

 notch, which admits the columella into this curious tympanic cavity, formed by the 

 scooping of the huge " otic process" {ot.p.) of this cartilage — the mandibular pier. The 

 next " pier" is specialised for auditory purposes, as the columella, and foregoes its liyoidean 

 (or lingual) functions (figs. 2, 3, 5, 8, 9, co.). 



The dorsal end pushes into the fenestra ovalis {f.o.), the membranous operculum of 

 which acquires a cartilaginous character, but its cells are thin, lunate, and concentrically 

 arranged, as in the sheath of the cranial notochord ; those of the rod itself are the 

 normal ovoidal corpuscles (fig. 9). Here I find a greater separateness of the stapedial 

 plate from the " mediostapedial" rod (fig. 9, m.st.,st.) than in any other " Sauropsidan." 

 Tlie rod itself is ossified largely ; the bony matter will reach farther outwards, and the 

 proximal plate also will become ossified. Its Batrachian condition is best seen now. 



