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Show 164 ON THE STRUCTURE OF 'l'IIE SKUJ.JT.J. nee t ed an upper al·ch, forminOo' part of tho. . brain- case, ,a n<l a I ower arc I1 w hi.ch enters into the c. omposition of the . face. ~rhe sides of this arch in the sectional vww are part~y constituted (cOin pare Fig. 48) by bones specially connected w~th t~e auditory apparatus, and the peduncle of the lower arch IS articulated "·ith these bones. The chamber contained within the lower arch, however, differs froin that seen in the section of tho hnman skull in that it is entirely devoted to the buccal cavity, and is not subdivided by processes of the palatine and maxil1ary bones into an upper: nasal, and a lower, oral, passag Fig. 66. Fig. 66.-The posterior segment of the skull of a Pike whieh has been Ye.rt.ically an.d transversely bisected. The bones of the inferior arch are represented <.lwgrammat.J· cally. The epiotic, opisthotic, pro-otic, and squamosal bones are left n~1sh~d e·~, as 111 the corresponding sect ion of the human skull. p .s.c., a.s.c., arrows Ill~Jcatlllg the positions of the posterior and external semicircular canals; x, parasphenotcl. The comparison of the transverse sections of the Pike's wi~h those of the l\tian's skull thus enables us to perceive certam resemblances between the two. In each there is an axis, upper and lower arches ; in each the section separates the bones which lodge the auditory organs ; and the most apparent difference between the two is the vastly gr ater proportionate size of the periotic bones in the Pike-\ 'l'IIliJ THUCTUHE OF 'rHE PIKE'S SKULL. 165 ~rhe comparison of the longitudinal section of the J\tlan's skull with that of tho Pike (Fig. 68) confirms the conclusions arrived at fron1 the study of the transverse sections. A "cranio- Fig. 67. Fig. o7 .-The anteriur segment of the skull represented in Fig. 66.-Mn, mandible. a.s.c., mTow indicating the position of the anterior semicircular canal. The letters B, S, one on each side of the basi-sphenoid, are seen through the canal for the orbital muscles. The pro-otic bone is left unshaded. Tn this, and iu the preceding figure, the dotted shading indicates cartilage; but, as the drawings were made from a tlry skull, it must be remembered that the whole of the cartilage entering into the cranium is not represented. facial axis," composed partly of bone and partly of cartilage, extends from the occipital foramen to the anterior extremity of the snout of the fish. The posterior part of this constitutes tho floor of the cranial cavity, and is the basi-cranial axis. The anterior part, excluded from the cranial cavity, is, as in l\fan, the basi-facial axis. Again, as in Man, three pair of chambers, . destined for the lodgment of the organs of the higher senses, are placed symmetrically upon the sides of the Pike's skull. The olfactory chambers are situated just in front of Prj, in ]..,ig. 65, and the orbits beneath S.Or., while the auditory organs are inclosed within the posterior bony walls of the brain-case: as indicated in the transverse sections. And, ns in Man, the olfaetory and |
