Immediately dorsocraniad of the external auditory meatus the zygomatic arch begins as the zygomatic process (_k_) of the temporal bone. On the cranial surface of the base of this process is the deep mandibular fossa (_l_) for the condyle of the mandible. This fossa is bounded caudally by the prominent postmandibular process (_m_). [Illustration: FIG. 40.--SKULL, SIDE VIEW. 1, occipital bone; 2, interparietal; 3, parietal; 4, temporal; 5, 5′, frontal; 6, malar; 7, sphenoid; 8, palatine; 9, presphenoid; 10, maxillary; 11, nasal; 12, premaxillary; 13, incisor teeth; 14, canine; 15, 16, 17, premolars; 18, molar. _a_, occipital condyle; _b_, external occipital crest; _c_, sagittal crest; _d_, lambdoidal ridge; _e_, tympanic bulla; _f_, jugular process; _g_, mastoid process; _h_, stylo-mastoid foramen; _i_, pit for tympanohyal bone; _j_, external auditory meatus; _k_, zygomatic process of temporal bone; _l_, mandibular fossa; _m_, postmandibular process; _n_, zygomatic process of the frontal; _o_, supraorbital margin; _p_, external pterygoid fossa; _q_, sphenopalatine foramen; _r_, orbital fissure; _s_, internal pterygoid fossa; _t_, hamulus; _u_, foramen ovale; _v_, foramen rotundum; _w_, optic foramen; _x_, opening of lachrymal canal; _y_, infraorbital foramen.] All that portion of the lateral surface of the skull which lies craniodorsad of the lambdoidal ridge may be divided (excluding the zygomatic arch) into three main parts, the =temporal fossa=, the =orbital fossa=, and the =face=. The boundaries of the temporal fossa have been given. The orbital fossa is bounded externally by a prominent semicircular ridge formed chiefly by the zygomatic arch, the zygomatic process of the frontal (_n_), and the supraorbital arch (_o_) of the frontal, which may be traced to the cranial root of the zygomatic arch. The orbital fossa may be considered to end caudally and ventrally at the level of the optic foramen (_w_); ventrad of it are certain smaller fossæ. Immediately ventrad is the long =external pterygoid fossa= (_p_), from which arises part of the external pterygoid muscle. This fossa begins at the sphenopalatine foramen (_q_) and extends caudad to the orbital fissure (_r_); it is separated by a ridge from the orbital fossa. Caudoventrad of the external pterygoid fossa and separated from it by a sharp ridge is the small narrow =internal pterygoid= fossa (_s_), which extends ventrad without interruption on to the surface of the hamulus (_t_) and caudad to within two or three millimeters of the tympanic bulla. From it the internal pterygoid muscle takes origin. The hamulus (_t_) projects caudoventrad in this region, forming a prominent feature in a lateral view.