_a_, squamous portion; _b_, petrous portion; _c_, _c′_, tympanic portion (_c_, entotympanic; _c′_, ectotympanic); _d_, zygomatic process; _e_, mastoid portion of the petrous; _f_, mandibular fossa; _g_, postmandibular process; _h_, tuberculum articulare; _i_, external auditory meatus; _j_, stylomastoid foramen; _k_, pit for tympanohyal bone; _l_, mastoid process; _m_, grooves bounding the jugular foramen; _n_, internal auditory meatus; _o_, appendicular fossa; _p_, hiatus facialis; _q_, styliform process of tympanic bulla.] The =squamous portion= (_a_) (=squama temporalis=) is thin and oval or has the form of an equilateral triangle with rounded angles, with a curved process, the =zygomatic process= (_d_), arising from its ventral border. Its outer surface (Fig. 22) is convex and smooth and gives origin to part of the temporal muscle. Its inner surface (Fig. 23) is concave and smooth except near the margins, where it is bevelled and rough. The roughened border is broader dorsad and caudad. The ventral margin of the bone is turned mediad at its cranial end so that the lateral face of the inverted portion looks ventrad. By this portion of its lateral face the squamous rests upon the tympanic bulla, and its edge articulates with the tentorium and the wing of the sphenoid. The remaining (caudal) portion of the ventral border overlies the mastoid portion (_e_) of the petrous. By the remainder of its border the bone articulates with the parietal dorsad and with the wing of the sphenoid craniad. The roughened portion of its inner surface overlies the margins of both these bones. The zygomatic process (_d_) is formed by the confluence of two roots. One of these starts from the ventral end of the lambdoidal ridge and passes along the ventral margin of the squama dorsad of the external auditory meatus. The other arises abruptly from the cranioventral angle of the bone. The process thus formed is at first broad and passes horizontally laterad and slightly craniad. It soon grows more slender and turns gradually craniad, while at the same time it twists so that the surface which is dorsal at the base becomes medial at the tip; the posterior root which is continuous with the caudal border at the base is continuous with the dorsal border at the apex. On the ventral surface of the base is a transversely elongated concave articular surface, the =mandibular fossa= (_f_), for the condyloid process of the lower jaw. Caudad of this is a sharp transverse ridge, the =postmandibular= or =postglenoid process= (_g_), and craniad of the lateral end of the fossa a slight tubercle, the =tuberculum articulare= (_h_). Near its apex the zygomatic process is more slender and its ventral border is bevelled for articulation with the malar or zygomatic bone.