The horizontal portion of this surface is oval, concave, rough, and forms the roof of the mouth, consisting of the palatine plates of the palate and upper maxillary bones, on which is seen a crucial suture, formed by the longitudinal and transverse palatine sutures. At the posterior and outer angles of this hori zontal portion are situated the posterior palatine canals and the grooves which proceed from them along the roof of the mouth ; on the inferior surface of the palate bones are ridges and depressions for the attachment of muscles, while behind the middle incisor teeth is placed the anterior palatine foramen. At the sides and in front the palatine arch is bounded by the alveolar border and teeth of the upper jaw, behind which descend the pterygoid pro cesses of the sphenoid and palate bones.
The inferior vertical division of this region is formed by the inner surface of the lower jaw and teeth ; it presents in front, along the median line, the inner mental ridge, and the genial processes; external to these the internal oblique lines, the sublingual and submaxillary fosse, the superior dental foramen, its groove and process; the condyles and angles of the jaw, its alveolar border and its base, which terminates it below, and near which, at the chin, are seen the depressions for the digastric muscles.
The lateral or zygomatic surfaces on each side are hounded above by the temporal border of the malar bone and by the zygomatic arch; in front by a line extended vertically from the external angular process of the frontal bone to the base of the lower jaw, and behind and below by the free border of the body and ramus of the inferior maxilla.
This region presents a superficial and a deep portion : the former comprises the lateral aspect of the malar bone, the zygomatic arch, and the external surface of the ramus of the jaw. On it we may remark, proceeding from above downwards, the temporal border of the malar bone and zygoma, forming the outer boundary of the temporal fossa; the external malar holes, the zygoma and its suture, which unites the malar and temporal bones; the inferior or masseteric border of the zygoma, the sigmoid notch of the lower jaw and the outer surface of its ramus, coronoid and condyloid processes and angle. The deeper division of this region presents the large zygomatic fossa, and is situated internal to the ramus of the jaw, which forms its outer boundary, and which must be removed to expose it completely : this done, the fossa is brought into view, bounded in front by the posterior surface of the upper jaw and part of the malar bone; superiorly by the inferior surface of the great wing of the sphe noid below its temporal ridge; at this part of the fossa are seen the spheno-temporal suture, the spinous process, and the spinous and oval foramina of the sphenoid bone. The narrow inner boundary is formed by the external ptery goid plate of the sphenoid ; behind and below the fossa is open. At the bottom of the zygo
matic fossa is situated the pterygo-maxillary fissure, forming the external orifice of the spheno-maxillary fossa, which is a Cavity situated between the tuberosity of the upper jaw in front, and the pterygoid process and palate bone behind : in this fossa are five holes, viz. three which open into it from behind, the foramen rotundum, the vidian or pterygoid, and the pterygo-palatine; one opening inter nally at the upper part; the spheno-palatine; one below, the upper orifice of the posterior palatine canal. The zygomatic fossa presents also at its upper and anterior part, the spheno maxillary fissure, which is directed from within outwards and forwards, and is formed inter nally by the orbitar processes of the palate and upper maxillary bones, externally by the orbitar plate of the sphenoid, and at its outer extremity, which is large, by the malar bone; it forms a communication between the orbit and the zygo matic fossa. Its inner end joins the sphenoidal and the pterygo-maxillary fissures, with the former of which it forms an acute, and with the latter, a right angle: thus these three fissures may be considered as branching from a common centre at the back of the orbit; they give passage to a number of vessels and nerves, and establish communications between the cavi_ ties of the face and cranium.
The superior or cranial region is very irregu lar, and is immoveably united to the cranium. It presents along the median line, from before backwards, the articulation of the nasal bone, with the nasal spine of the frontal, the union of this spine with the perpendicular plate of the ethmoid, the articulation of this plate with the vomer, the articulation of the voiner with the sphenoid.
Along the sides, from within outwards, are seen the arched roof of the nasal fossa formed in front of the nasal bones, in the middle by the cribriform plate of the ethmoid, and behind by the body of the sphenoid. External to these parts are found the base of the pterygoid process, the articulation of the palate with the body of the sphenoid bone, the pterygo-palatine canal, the spheoo-palatine foramen ; next the spongy masses of the ethmoid united behind with the sphenoid, and anteriorly with the os frontis; and still more forwards are seen the articula tions of this bone with the lachrymal, upper maxillary, and nasal. To the outer side of these articulations is the triangular roof of the orbit, limited externally by the sphenoid and malar bones and by the sphenoidal fissure. Next may be observed the orbitar plates of the sphenoid, forming the greater part of the outer wall of the orbit, and lastly the zygoma. The inner border of the orbitar plate of the frontal bone presents the fronto-lachrymal and the frontal-ethmoidal sutures; the outer border the spheno-frontal and fronto-jugal sutures.