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Show 176 ON 'fHE STRUCTURE OF •rJIE :SKULL. ~rhe principal bones which. snrr~und th or~l ca~it~ in thr Pike are di posed, as ju Man, In pa1rs, eon1 b 111~)· In front of and above the oral aperture, while oth rs arc behind and below that aperture; and they inclo , tho bucral aud pharyngeal chainbers. Fig. 71. FiO', 71.-Palato-quadrate arch, with tl1c hyomandihnlar nnll symplretic, the articular " piece of the lower jaw, atHl Meckel's cat tilage, of the Pike, seen from tl1e inner side. a, the cartilnge interpo_sed. between the hyoman_rlil.Hllar and the symp!cctic; b, that which serves as a pediCle for the pterygl1-palatme arch; c, process of the hyomandibnlar with which the operculum articulates; d, head or the hyomamlil.mlar which articulates with the side of the sl·u ll. The anterior pair of I r -oral b ne (Pnu:c. I! ig. G.:>), small, and beset with t eth upon th ir under- ·urfacc , ar connected with the vomer aud th termination of the cartilaginous rostrmu formed by the int rnasal eptu1n. They obriou ly an. w r to the buman pre-maxilL. ,. An elongat cl bon (.lJ.E '.), whi ·h bears no teeth, i connected anteriorly with th 1 r -nntxilla, and, lying extermtl to th other pro-oral bon ) fonn the boundary of the gape. Its hornology with th } 1naxilla f l\1an app ar to be unquestionable. A second sn1all r bone i conn) ·ted with the po terior part of the upp r edo·o of the 1naxilla, and i., nsnally regarded n. a subdivision of it. Behind t.h 1 rc-maxillo , nd int rnal t tho maxillm, in tho ·ituation occupi d by the p<tlatin and pterygoid bonos in Man, the Pike ha an os eou arch of nnlCh greater c01nplexity and omewhat differ nt nn ction . The ·mnmit of thi. ' palato-quadrate" arch is moveably arti(•ulat d, by a cartilao·inou.· pedicle, with tho outer, urfare of tho pro-frontn.l 1roc . , · of th RkulL The' anterior crus of tl1r THE STRUCTURE OF THE PIKE'S SKUIJL. 177 arch. stre~ches for':ards, parallel with the vomer, to th prenlaxilla; ~ts postenor crus extends backwards, and, spreading out, e?ds In an upper (Mpt.) and a lower ( Qu.) prolongation. ~rve bones enter into the composition of the arch-two med~an, two posterior, and one anterjor. Tho medjan bones are so dispo~ed .that their. anterior ends embrace the lower part of the cartlla?rnous pedwle (b), the one lying more external, and the other Internal, to the latter. The more external has been calle~l "ectopterygoid." * It exhibits a short, ascending process, ru1~nmg up t~wards the pre-frontal, and strengthening the cartilaginous pechcle ; an anterior process which articulates with the bone Pl.; and a posterior arched prolongation, which descends in front. of the bone Qu., and articulates with its anterior edge. The. Internal bone, called '~ entopterygoid" (Ept.), is a nearly str~1ght, flat bone, the antenor half of which is applied, like a sphnt, to the inner face of the ectopterygoirl, while its broader posterior face is similarly adjusted, above, to the bone Mpt., and, below, to the bone Qu. The two last··mentionod " posterior " bones of the arch are termed respectively the "metapterygoid" and the "quadrate" bones. The former is a broad, four-sided bone, convex upon' its inner suriace, which presents a raised curved ridge, beneath which the entopterygoicl is received anteriorly and the hymnandibular posteriorly. It is connected below. with the quadrate bone, and, behind, it overlaps the hyomandibular (H.M) and the symplectic (By.). The os qnaclratnm ( Qu. ), so termed, not on account of its form, which is triangular, but by reason of its identity with a ?one. called by the same name in Birds and Reptiles, presentH Inferwrly an articular head, with an elongated articular surface, convex from before backwards, for the lower jaw. On the posterior part of its inner sudace it has a deep groove, directed from a~ove downwards, very nearly parallel to its posterior edge. Into this the symplectic is received. The anterior bone (Pa.), lastly, is elongated and flattened, and bears teeth upon its lower surface. It iR received ante- * N?t to. mu~tip~y names unnecessarily, I adopt this term, which involves no· theoretiCal I~phcatwns. It must be carefully borne in mind, however, that this "eetoptorygmd " has nothing to do with the " external pterygoid" process of Man. N |