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Show .116 ON THE VERTEBRATE SKULJ,, parts,-an upper, divided into two by t: 1nedian septum, the nasal passages ; and a lower, the orral cavdy. The posterior portion of the bisedcd skull (Fjg. 48) presents, in like manner, a strong floor (BO) and a large upper chaml>or for the lodgment of parts of the brain; bnt tho lower cha1nbor seems at :first to be absent in the skeleton, being represented, in fact, only by the styloid processes (St), the o-called stylohyoid ligarnents, and the hyoidean bone (Hy) which is suspended by these ligaments to tho sknll. Fig. 49. lfig. 49.-:---:-The posterior half of the tmnsversely bisected skull, Fig. 48.-JJ.O., the b::~siocclpltal; E. 0., E. 0., the ex-occipitals; 1', the temporal hon left in outli ne; O.F., occipital .foramen; VII., canal for the portio dura aml portio mollis; IX., foramen for the mnth or hypoglossal nerve. A longitudinal and vertical section of the skull (Fjg. 50) enables~ us to observe the same relations of the parts from another point of view. The central bones (BO, BS, PS, Eth., Vo), which lie between the arches of the brain-case above, and the arches of the face b low, are, 111 such a section, found to THE STRUCTURE OF THE HUMAN SI<ULL. 117 constitute. a continu?us series, fi·om the occipital foramen to the anterwr extremity of the nasal passage, which, as it fm·ms the comruon centre or axis, not only for the bones of the brain- Fig. 50. _POJ. Fig. 50 .-Lo? ~itudi.nal and \' eJ.tical section of a Human Skull.-* The sella tnrdca, Au. The pos1t10~ ~~ the ~upenor and postenor vertical semicircular canals. I., [[., V., Y_III., IX. I he ex1t of the olfactory, optic, third division of the fifth eighth and mnth nerves. Vo., the Y omer. ' ' case or cranium proper, but also for those of the face, may be termed the Craniofacial amis. It will be useful to divide this axis iuto two portions,-a |
