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Show 124 ON THE VERTEBRATE SKULL. Eh .1" . " . are called '' lateral 1nasses of the ~t mOI: ' or supenor ann middle spongy bones,'' and more ImmedJ atcly by the perforated cribrifonn plate, which allows of the passage of the :filaments of the olfactory nerve, and connects these lateral masses whh the larnina perpendicularis, or proper ethmoid. Looking at the bones vvhich form the imn1ediate .walls of the upper and middle part of the nasal chambers, w1t h reference onlv to the olfactory organs, we might "'ay, in fact , that the ant~rior vacuity of the cranium proper is stopped by the ossified walls of the olfactory sacs, consisting of the ethmoid and vomer in the middle line, of tho superior and middle spongy bones (or so-called lateral masses of the ethmoid) supero-laterally, of the inferior turbinal Lones infero-laterally. And to these ossifications must be add d, as 1ne1noers of the olfactory group, the bones of B rtin, po teriorly and superiorly, and the nasal bones, anteriorly and "uperiorly. rrhe great posterior vacuity on each .: ide i filled up by the Temporal bone, which consists of a very considerable nnmber of distinct elements, only distingui hable by eli section and by the study of development in 1\Ian, but which remain permanently di." tinct, and undergo v ry strange 1netamorphoses in n1any of the lower Vert brutes. Some of th so constituents of the temporal bon , such as the squamou portion or Sqtt~amosal (Sq.), and the ll1.alleus, I ncus, and Stapes, are discrim inated by the tudent of ordinary ln1n1an mwton1y; but there are 1nany other which he i not in the habit of r gnrding as distinct osseous el ment.... Thu the bony " xternal auditory meatus" is primitively a di tinct bon , t rm d Tympanic (Ty.) on account of its affording th frame in which almost the whole of the tympanic membrane is t . rrhe Styloid process (St.) is originally a distinct bon . And, la t1y, the pars petrosa and pars mastoidea of human anatomy ar , in reality, made up of three distinct o'" ifications, of whi ·h I shall have to say more presently, but which I hall F ak of for the present under the colleetive na1no of the P e?,·iotio bon ,', b au e they immediately surround tho organ of h aring. Not m rely the p rioti , but also the quamosal and tym· panic bon , · are o cl s ly r 1at d to tho ancl itory organ, that THE STHUOTUTIE OF THE HUMAN SKULL, 125 the postero-lateral apertures of the cranimn· mnv be said to ?e stopped by the osseous chambers of the ~uditory organ, In the same way as the anterior apertures are closed by the osseous chambers of the olfactory organs. As the eye is contained only in a mobile fibrous capsule, the sclerotic, the apertures which lead to the orbit-the spheno-orbital fissures and the optic foramina-are not closed by any special bones pertaining to the sensory organ lodged therein. rrhus the brain-case may be said to be composed of three superior arches connected respectively with the three divisions of the basi-cranial axis, and of two pair-an anterior and a posterior-of bony sense capsules interposed between these arches. A middle, third pair of sense capsules is not represented by bone in the cranial walls. In like manner, the face may be resolved into a series of bones, occurring in pairs from before baekwards, and forming more or less well-de:fined lower arches, some of which embrace the nasal cavity, being placed in front of, or above, the oral aperture, while others enclose the buccal chamber, and are situated behind and below the oral aperture. Of the former, pre-oral bones, there are four pairs--the Prmnaxillm (Pmx. ), the Maxillm (Mx.), the Palatines (Pl.), and the Pterygoids (Pt.). The Premaxillm, which lodge the upper incisor teeth, so early lose their distinctness in manr by becoming anchylosed with the maxillary bones (at any rate externally and anteriorly) that they are rarely reeognised as separate bones. N evertheless, a suture extending upon the bony palate fro1n the posterior n1argin of the alveolus of the outer incisors to the incisive foramen, very commonly persists, as an indication of the primitive separation of these bones. 1'he most important character of the premaxilloo, regarded morphologically, is, that they are connected, superiorily, with the anterior termination of the cranio-facial axis, and that this connection is a primary one. Each premaxilla passes from its inner end, wLich is united with the axis, outwards and backwards, and two of the other three pair of pre-oral bones have similar relations to the cranio-facial axis. Th~ anterior of these are the Palatine bones; the inner, or sphenoidal, processes of which are connected with the basi- |
