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Show 122 ON THE VERTEBRATE SKULL. . 1 f' this spot down wards and forwards, to tho obhque y rom ' . h . l . · (F' 53) on the under-surface of t e ax1 , w 1ere 1ts ear-pmnt e 1g. ·1 · · . 1 b es continuous with the osseo- art1 ag1nous Inter-ti age ecom uasal septum. It is this osseo-cartilaginous septu~ betw e~1 the two n~sal cavities, the upper free edge of which constitutes the c~2sta galli, while the lower fr.ee ~dge ~upports the septum nanum, which terminates the bas2jac2al aons. All the upper and middle part of thi ptum is formed by a thin osseous plate, t.h lamina perpendicularis of human anatomy, or true Ethmoid (Eth.), which abuts, in front, upon the frontal and nasal hones; behind, upon the presphenoid; and below, upon a rod-like mass of cartilage, which becomes connected with the septum narium and th premaxillary bones anteriorly and inferiorly, and i oblit rated with ago. The inferior and posterior part of the or hun is constituted by a bone with a gutter-like uppe~~ an? ant rior b~undary, which embraces the whole round d 1nf nor and postenor edge of the cartilage in question, and thus xt n is fron1 the undersurface of the basi-sphenoid, p steriorly an l superiorly, to the 1niddle of the roof of the bony palat , anteriorly and inferiorly. r:rhis bone is the Varner (Vo., Fig. 50). Thus there are thre b ncs in the basi-m·anial awis,-the basi-occipital, basi-sph noid, anJ pre ph n id; and there are two bones in the basi-facial axi ,-th ethmoid and the vomer; the essential differen e betw en th two set of bones being that the form r onstitute th 1niddl 1 art of the floor of the brain-case, while the latt r ar alt geth r excluded there-from. We may now turn to th upper arch s of the skull, or thooo bones which form the walls and roof of the brain-case. In the young skull from whi h th Fjgur 52 an 1 53 are ~aken, t?e postero-lateral margins of th ba i-oceipital are un1t~d ~v~th the rest of the occipital bon , only y . ynchondr~s1s .. ~he parts of the latter whi h ar thus unit d with the basi-OCClpJtal, and which limit the side f th great occ·ipital foramen, are primitively distinct lJou s,-the Ew-occipitals (Eo.); while the THE S'l'RUOTUI~E OF 'l'lJE 11 MA LL. squamous part, which bounds the p st rior nt f the foramen, is known as th ) Supra-occipital ( o, Bo'). 11 th \ · bones, eventually beco1ning an ·hylo d t cr th '1' £ nn th ~ occipital bone of the human ann.tomi. -t; or what w me Y t nn the first, posterior, or Occipital segment f the .·kull. From the sides of the basi-sphenoid, external to th lingulw two wide processes, well-known as the "grec t r wing f tll sphenoid" or Alisphenoids (AS) spring, and unit ·uturally with the expanded Parietal hones (Pa), which form the l 111 - like crown of the skull, and unite in the middle line in th sagittal suture. In this way a second, n1iddlo, or 1 arietal segment of the skull is distinguishable. In like manner, the presphenoid passes, on each ide, int the smaller processes, the "lesser wings of the ph noid '' alte minores, or wings of Ingrassias ; which, on ac ount of th ir relations to the orbits, have been well named the Orbitosphenoids (OS). And these, externally and anteriorly, unit by suture with the arched and expanded Frontal bone (F-;·), originally double, and separated by a median frontal utur which ordinarily early disappears. These bonet:) not only m i in front, but send in processes which roof over th orbit · and unite with the free anterior edges of the oTbito-sphenoid , thu · leaving only a long and narrow vacuity, on each side f the crista galli, and in front of the presphenoid. The presphenoid, the orbito-sphenoid, and the frontal are the constituents of the third, anterior, or Frontal segm.ent of the skull. It will be observed, however, that this enun1eration f the bones of the three great segments of tl1e skull does not account ~or .all the ~istin?t osseous elements, which enter, directly and 1nduectly, Into Its boundaries. If all the bones m ntion d are put together, there still remain four considerable vacuiti ·; two small, already mentioned, in the proper front wall of the skull, . on each side of the crista galli; and one on ea h side, postenorly, between the occipital and parietal segments, of very .much l~~ger size, and extremely irregulal' form. Th an~enor :acuities ar.e filled up by those spongy osseous masses, united With the lam2na perpendicularis in the adult skull, whi h |