The circumference of the squamous process is sharp, in all that part which is above the level of' the zygomatic process, and denticu lated, at the expense of its outer table, in the rest of its extent ; so that it rests on the sphe noid bone.
The connexions of this bone and the me chanical effects which result from its position, will be readily understood. Its petrous por tion being wedged between the basilar process of the occipital bone, which serves it as a fulcrum, and the ala major of the sphenoid, which binds it against that fulcrum ; the in ferior part of its squamous process resting on, and being sustained by the sphenoid bone, while its mastoid process is braced in by the posterior inferior angle of the parietal, and by the occipital bone— the fronting squamous margin will effectually resist the lateral thrust of the parietal; the more so that a limited yielding movement is allowed at the fulcrum. The zygomatic process advancing forwards to the malar bone, will, with its fellow of the opposite side, give stability to the several bones of the face ; and, in common with the pterygoid processes of the sphenoid bone, maintain the integrity of the various arches which they form. It is also connected with the lower jaw.
This bone is developed from six points of ossification : viz. one for each of the three great divisions, and one each for the zygomatic and styloid processes and the auditory canal. At birth it consists of four pieces, the squa mous (a), mastoid (c), petrous, and an in complete bony ring (d), to whiCh .the mem brane of the tympanum is attached. The bony ring is the first to join, by its upper part, the squamous; after which it is consolidated with the petrous, and then extends itself out wards and backwards to form the meatus auditorius externus, and all the four pieces are then united. In infancy the bone sustains great changes ; the squamous process from being straight becomes curved ; the zygomatic process recedes from the squamous and in creases tile space between them ; the mastoid portion becomes more tumid, is developed upwards and backwards, and sends fbrth the nipple-like process which gives to it its name.
The eminentia articularis and fossa articularis from an oblique assume a transverse direction, and become, the one more concave, the other more convex. The styloid process, though ossified in its middle, is frequently, to an ad vanced age, connected with the bone by carti lage only.
The parietal bone (os parietale; Germ. die Scheitelbeineoder Seitenbeine) (jig.372, 373 P) constitutes with its fellow the greater portion of the vault of the skull, and forms with it a sort of bridge, the corners of which on each side are fixed, the one on the great wing of the sphenoid, the other on the mastoid proces3 of the temporal bone, the squamous procesS of which braces in the intervening space.
The external suilace offers in its centre a prominence which marks the spot at which ossification commenced; and it marks also the widest part of the skull. Below this is a semicircular line (the linea temporalis); to which are attached the temporal fascia and muscle; still more inferiorly is a plane surface occupied by the temporal muscle; and be tween it and the lower border, is a inflated articular portion with converging strite, to- be applied against the squamous portion of the temporal bone. Near the posterior part of the bone and a little removed from its upper border is the. foranzen parietale, for the passage of a vein to the longitudinal sinus.
The inner surface exhibits the usual indi cations of the convolutions of tlie brain, and also arboreseent sulci, which mainly proceed from the anterior inferior angle of the bone, and are directed upwards and backwards to the fossa panietalis, which answers to the pa rietal prominence on the outer surface; these sulci lodge the branches of the middle menin geal artery. Along the upper border is a de pression, which, with a shnilarly disposed edge of the other bone, forms a groove for the lodgement of the longitudinal sinus,, and hence is termed sulcus longitudinalis ; near to it are sometimes seen small depressions (foss& Pacchionii) for the granulations of the dura mater, called glandulw Pacchioriii externm.