The lateral region (fig. 373) is oval, and its boundaries have already been stated. Its sur face, lengthwise, is undulated, being convex behind, where the temporal and parietal form it; and concave in front, where the temporal and sphenoidal enter into its composition. Pro ceeding from above downwards, and com mencing with the linea temporalis, we have so much of the parietal and frontal bones as are below that line, with the inferior extremity of the coronal suture between them; next, the sutura squamosa between the parietal and temporal bones, and part of the transverse suture between the frontal and sphenoid ; below this, the squamous process of the tem poral bone, and, in front of it, the temporal process of the sphenoid with the line of arti culation between them. These parts form the fossa temporalis, which is limited inferiorly, on the sphenoid by a crest which divides it from the jugal fossa belonging ta the face, and on the temporal by a groove on the upper part of the two roots of the zygomatic process, in which play the posterior horizontal fibres of the temporal muscle. Passing from behind forwards, there. will be observed at the lower boundary of this region, the additamentum suturce squamosze ; the base of the mastoid process; the foramen auditorium externum ; and, lastly, the zygomatic process of the tem-. poral bone articulating anteriorly with the molar bone.
The interior of the cranium presents through out its entire extent more or less evidence of the adaptation of its surface to the convolutions of the brain.
The base is bounded, in front by the fora men conum ; behind, by the centre of the internal crucial spine ; and, in its circtunfe rence, by a line passing on each side along the outer border of the orbitar process of the frontal bone, the junction of the parietal and sphenoid; the parietal and temporal bones; and the lateral limb of the internal crucial spine of the occipital.
It is placed obliquely downwards and back wards, and consists of three principal divisions or platforms—the posterior being the lowest, the anterior the highest; and the middle, on a plane between the two.
The anterior division is called the anterior fossil?, and sustains the anterior lobes of the brain. It is concave in the middle and con vex on each side; it is limited, anteriorly by the merging of the orbitar processes into the general mass of the frontal bone, and poste riorly by the posterior margin of the mi nores. On the median line, from before back wards, we encounter the foramen ccecum ; the crista galli; the ethmoidal process of the sphenoid bone ; and, lastly, the smooth sur face of that bone on which the olfactory nerves repose. On either side of the crista galli is the processus cribrosus, with its foramina, and slit for the ethmoidal nerve and vessels ; more outwardly, is the transverse suture uniting this process to the frontal bone, and in it may be seen the internal orifice of the anterior internal orbitar foramen. From hence outwards, is the orbitar process of the frontal bone, somewhat arched, and displaying, more evidently than in the rest of the skull, the digital impressions of the brain ; behind this is the transverse suture uniting it to the small wings of the sphenoid bone; and, lastly, there is the upper surface of the small wings themselves.
The midd/cfbssee consist of two large fossm laterally, and one, which is smaller, centrally. This latter is the pituitary fossa; in its front is the olivary, and, behind it, is the basilar process ; on its sides are the sulci carotici, and its corners are bounded by the ephippial or clinoid processes. In front of the olivary process is the groove on which the optic nerves decussate; and between it and the anterior ephippial processes of each side is the foramen opticum.
The lateral fossze are very deep and of an irregular triangular figure, the base of which is directed outwards. Anteriorly they are bounded by the small wings of the sphenoid bone, and posteriorly by the ridge which se parates the cerebral from the cerebellar surfa.ce of the petrous portion of the temporal bone. Each is formed, anteriorly and internally, by the great wing of the sphenoid ; posteriorly, by the cerebral surface of the petrous process; and, externally, by the squamous process of the temporal bone. In it are seen the lines of junction between these parts, and the sulci formed by the spinous artery of the dura mater. At its anterior boundary there is the foramen lacerum orbitale superius ; and behind it, inclining gradually outwards, there are in suc cession, the foramen rotundum, the foramen ovale, the foramen spinale, the sulcus Vidi anus, the hiatus Fallopii, the depression for the Gasserian ganglion, and the processus semi circularis. To the inner side of this range, and on a level with the foramen ovale, is the foramen lacerum anterius.
The posterior division extends from the basilar process of the sphenoid bone to the internal tubercle of the occiput. Its margin is of a triangular figure, with its base curved and directed backwards. The petrosal ridges form the sides of the triangle, and the lateral limbs of the internal crucial spine, its base. On the median line and passing backwards we observe the superior sulcated surface of the basilar process, with a groove on each side for the basilar sinus ; the fbramen magnum with the anterior condyloid foramina near its ante rior part; and, lastly, the inferior limb of the internal crucial spine, separating the two great cerebellar fossm. Each of the latter is bounded, above and to the outside, by a broad groove for the lateral sinus, which groove passes from the occipital bone to the mastoid angle of the parietal, from thence to the mastoid process of the temporal (where the mastoid foramen opens into it), and, ulti mately, to the occipital bone again, where it turns forwards to the foramen lacerum pos terius. In this groove is seen the termination of the lambdoidal suture, and the additamentum suturm squamosoe and the additamentum su turw lambdoidalis cross it ; the principal portion of the latter being seen in the cere bellar fossa. Anteriorly, and above the fora men lacenim posterius, is the cerebellar surface of the petrous process of the temporal bone ; exhibiting the openings of the meatus audi torius internus and of the aqueduct of the vestibule ; and, on the ridge which separates this from the cerebral surface, the groove for the petrosal sinus.