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THE SKULL, FROM
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THE See also:SKULL, FROM BELOW (norma basalis) (fig. 4). Starting from in front, the See also:superior alveolar See also:arcade with the See also:teeth sockets is seen. This in a See also:European skull approaches a semicircle, but in See also:lower races the sides become more parallel; this is known as a hypsiloid arcade. Within the arcade is the hard See also:palate formed by the maxillae in front (fig. 4, m), and the palate bones (p) behind. At the front of the median suture between the maxillae is the anterior See also:palatine See also:canal which, if it is looked into closely, will be seen to See also:lead into four small foramina, two antero-posterior known as Scar pa's foramina, for the naso-palatine nerves, and two lateral called Stensen's foramina for small See also:arteries and the re-mains of the mouth opening of Jacobson's See also:organ (see OLFACTORY See also:SYSTEM). In See also:young skulls a suture runs outward from the anterior palatine canal to between the lateral incisor and canine sockets, and sometimes another runs from the same See also:place to between the central and lateral incisor teeth. At each postero-lateral See also:angle of the palate are the posterior palatine canals for the descending palatine nerves. The posterior See also:mar-See also:gin of the hard palate is a See also:free edge which forms the lower boundary of the posterior nasal apertures or choanae and attaches the soft palate (see PHARYNX). Be-See also:hind the alveolar arcade on each See also:side are the See also:external and See also:internal pterygoid plates of the sphenoid; the external is a See also:muscular See also:process for the See also:attachment of the pterygoid muscles, while the internal ends below in the See also:hook-like hamular process which is directed backward and outward. Dividing the posterior nasal See also:aperture into two is the See also:vertical hind edge of the vomer (v), which articulates above with the See also:body of the sphenoid (basi-sphenoid), and just behind this the sphenoid is See also:united by See also:bone with the basioccipital (b), though up to twenty years of See also:age there is a synchrondrosis (see See also:JOINTS) called the basilar suture) between them. It is therefore very easy to tell an adult's skull from that of a young See also:person. Passing back in the See also:mid See also:line the foramen magnum (f) is seen, through which pass the See also:spinal See also:cord and its membranes, the vertebral arteries and the spinal See also:accessory nerves. A little in front of this is a small tubercle, the pharyngeal spine, to which the constrictors of the pharynx are attached. On each side of the fora-men magnum and in front of its mid transverse See also:diameter are the condyles (c), which articulate with the See also:atlas, while just above these are the anterior condylar foramina, one on each side, for the exit of the hypoglossal nerves. External to the pterygoid plates the See also:base of the skull is formed by the See also:ali-sphenoid, which projects backward into a point, the spine of the sphenoid, and just in front of this is the small foramen spinosum for the passage of the See also:middle meningeal artery. In front and a little internal to the foramen spinosum is a larger opening, the foramen ovale, through which the third See also:division of the fifth See also:nerve leaves the skull. Into the re-entering angle between the ali-sphenoid and basi-occipital is fitted the petrous See also:part of the temporal, which, however, does not quite fill the See also:gap but leaves a space on each side of the site of the basilar suture to be closed in by fibro-See also:cartilage, and this is known as the middle lacerated foramen. On the lower See also:surface of the petrous bone is the See also:round opening of the See also:carotid canal through which the internal carotid artery and its accompanying sympathetic nerves pass into the skull, while more externally the styloid process projects downward and forward and is more or less ensheathed at its See also:root by the rampart-like See also:ridge of the vaginal process. Between the styloid process and the occipital condyle lies the jugular or posterior lacerated foramen through which pass the lateral and inferior petrosal sinuses, and the glosso-pharyngeal, vagus and spinal accessory nerves. The bone which See also:bounds this foramen behind, and which bears the posterior two-thirds of the occipital condyle, is the ex-occipital part of the occipital. A little behind and external to the styloid process is the tip of the mastoid process, just internal to which is the deep antero-posterior groove for the digastric muscle, and internal to that another slighter groove for the occipital artery. Behind the styloid process and between it and the mastoid is. the stylo-mastoid foramen through which the facial nerve passes, while in front of the process the glenoid cavity can be seen in its entirety, hounded in front by the eminentia articularis and divided into an anterior articular part and a posterior tympanic See also:plate by the Glaserian fissure. Just internal to the glenoid cavity is the opening of the bony Eustachian See also:tube. The posterior part of the norma basalis behind the foramen magnum is formed by the supra-occipital part of the occipital bone, so that all the four parts of the bone, which are See also:separate up to the third See also:year, help in the formation of that large opening. Between the foramen magnum and the external occipital protuberance and superior curved line already noticed, the bone attaches the deep muscles of the See also:neck. Additional information and CommentsThere are no comments yet for this article.
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