The external or zygomato-maxillary surface is rough in front, where it rests against the upper maxillary bone ; behind this the lower two-thirds are marked by a groove, which, in conjunction with one on the upper maxillary bone, forms the posterior palatine canal. Above this, the bone is smooth, and forms the inner and deep part of the pterygo-maxillary fissure.
The anterior border, thin and projecting, forms a process (the maxillary) which is re ceived into the fissure in the lower edge of the orifice of the maxillary sinus.
The posterior or pterygoid border is united to the anterior border of the pterygoid process of the sphenoid : below, it becomes broad and is continued along a process which stands downwards, outwards, and backwards, from the angle of union of the posterior borders of the vertical and horizontal plates of the hone. This process is the plerygoid or pyramidal, and presents three grooves behind, viz. one internal and one cxtirnal, (of which the inner is the deeper,) for the reception of the anterior borders of the lower extremity of the pterygoid plates; and a middle triangular groove extending high up, and which forms a part of the pterygoid fossa. The outer surface of this process is rough, and is articulated with the upper maxillary bone : its apex is continuous with the external pterygoid plate.
The irfcrior border is united to the horizon tal plate.
The superior border presents a deep semi circular notch (sometimes a hole), which with the sphenoid bone above forms the spheno palatinefimainen. This notch divides the upper border into two processes, 1. the posterior (the sphenoidal); 2. the anterior (the orbitar). The sphenoidal process is curved inwards and back wards, and has three surfaces, 1. an internal or nasal, forming part of the cavity of the nose; 2. an external, which forms below the splieno palatine foramen the deep wall of the pterygo maxillary fissure ; 3. an upper, which is con cave and rests against the body of the sphenoid bone, and contributes to the pterygo-palatine canal.
The orbitar process stands upwards and outwards on a narrow neck, and presents five surfaces. 1. The anterior (or maxillary) arti culates with the upper maxillary hone. 2. The internal (or ethmoidal) forms a cell which unites with those of the ethmoid. 3. A posterior
(or sphenoidal) presents a cell uniting with the sphenoid, and communicating with its sinuses. 4. The superior (or orbitar), which is smooth and contributes to form the floor of the orbit: its posterior border forms a part of the spheno maxillary fissure, and separates the orbiter sur face from, 5. the external or zygomatic, which looks into the pterygo-maxillary fissure.
Connexions.— Each palate bone articulates with five bones, viz. two of the cranium, the sphenoid and the ethmoid ; and with three of the face, the upper maxillary, the inferior turbi nated, and the vomer, besides its fellow bone of the opposite side. It is lined with the buccal and pituitary membrane. It contributes to form the cavities of the mouth, nose, and orbit ; the pterygo-maxillary fissure, and the zygomatic and pterygoid fosse'. It gives attachment to the soft palate, and passage to the spheno-palatine, pterygo-palatine, and posterior palatine vessels and nerves ; also to the two pterygoid muscles, the eircumflexus palati, the levator uvulre, the palato-glossus, and the palato-pharyngeus.
The structure is compact, except at its pte rygoid process, where it is cancellous.
Developement.—It is complete at birth, ex cept that the vertical plate is short to corre spond with the short vertical diameter of the upper maxillary. About the third month ossification appears in a single point, at the junction of the two plates with the pyramidal process.
Molar bones (ossa make v. mutat od V. tygth wawa ; Fr. os de la porn:nate ; Gem. die Jochbeine oder Backenbeinc).—These bones, corresponding in situation to the prominence of the cheeks, are somewhat of a quadrilateral figure. Each presents three surfaces; 1. an external or facial; 2. an internal or temporo xygornatic; 3. a superior or orbiter. There are besides four borders and four angles.
The facial surface forms the eminence of the cheek, looks outwards and forwards, is smooth and slightly convex in front, and is marked by one or more small holes (molar jinvonina), which give passage to vessels and nerves. It is covered above by the integuments and the orbi cularis palpebrarum, and below and externally it gives attachment to the zygomatic muscles.