THE MAXILLA 87 



Blood-supply. — Arteries are supplied to this bone by the nasal branch of the ophthalmic, 

 the frontal, the angular, and the anterior ethmoidal arteries. 



Articulations. — With the frontal, maxilla, ethmoid, and its fellow of the opposite side. 



Ossification. — -Each nasal bone is developed from a single centre which appears about the 

 eighth week in the membrane overlying the fronto-nasal cartilage. The cartilage, which is 

 continuous with the ethmoid cartilage above and the lateral cartilage of the nose below, sub- 

 sequently undergoes absorption as a result of the pressm-e caused by the expanding bone. At 

 birth the nasal bones are nearly as wide as they are long, whereas in the adult the length is 

 three times greater than the width. 



THE MAXILLA 



The maxilla or upper jaw-bone (figs. 109, 110, 111) is one of the largest and 

 most important of the bones of the face. It supports the maxillary teeth and 

 takes part in the formation of the orbit, the hard palate, and the nasal fossa. 

 It is divisible into a body and four processes, of which two — the frontal and 

 zygomatic — belong to the upper part, and the palatine and alveolar to the lower 

 part of the bone. 



The body is somewhat pyramidal in shape and hollowed by a large cavity 

 known as the sinus maxillaris (antrum of Highmore) , lined by mucous membrane 

 in the recent state, and opening at the base of the pyramid into the nasal cavity, 

 the zygomatic process forming the apex. The anterior (or facial) surface 

 looks forward and outward and is marked at its lower part by a series of eminences 

 which indicate the positions of the fangs of the teeth. The eminence produced 

 by the fang of the canine tooth is very prominent and separates two fossae. 

 That on the medial side is the incisive fossa, and gives origin to the alar and 

 transverse 'portions of the nasalis, and just above the socket of the lateral incisor 

 tooth, to a slip of the orbicularis oris; on the lateral side is the canine fossa, from 

 which the caninus {levator anguli oris) arises. Above the canine fossa, and close 

 to the margin of the orbit, is the infra-orbital foramen, through which the terminal 

 branches of the infra-orbital nerve and vessels emerge, and from the ridge im- 

 mediately above the foramen the quadratus lahii superioris takes origin. The 

 medial margin of the anterior surface is deeply concave, forming the nasal notch, 

 and is prolonged below into the anterior nasal spine. 



A ridge of bone extending upward from the socket of the first molar tooth 

 separates the anterior from the infratemporal (zygomatic) surface. This latter 

 surface is convex and presents near the middle the orifices of the posterior 

 alveolar canals, transmitting the posterior alveolar vessels and nerves. The 

 posterior inferior angle, known as the tuberosity [tuber maxillare], is rough and is 

 most prominent after eruption of the wisdom tooth. It gives attachment to a 

 few fibres of the internal pterygoid muscle and articulates with the tuberosity of 

 the palate. 



The orbital surface [planum orbitale] is smooth, irregularly triangular, and 

 forms the greater part of the floor of the orbit. 



Anteriorly, it is rounded and reaches the orbital circumference for a short distance at the 

 root of^the nasal process; laterally is the rough surface for the zygomatic bone. The posterior 

 border, smooth and rounded, forms the inferior boundary of the inferior orbital fissure. The 

 medial border is nearly straight and presents behind the frontal process, a smooth rounded 

 angle forming part of the circumference of the orbital orifice of the naso-lacrimal canal, and a 

 notch which receives the lacrimal bone. The rest of the medial border is rough for articulation 

 with the lamina papyracea of the ethmoid and orbital process of the palate bone. 



The orbital surface is traversed by the infra-orbital groove, which, com- 

 mencing at the posterior border, deepens as it passes forward and finally becomes 

 closed in to form the infra-orbital canal. It transmits the second division of the 

 fifth nerve and the infra-orbital vessels and terminates on the anterior surface 

 immediately below the margin of the orbit. From the infra-orbital, other canals 

 — the anterior and middle alveolar — run downward in the wall of the antrum and 

 transmit the anterior and middle alveolar vessels and nerves. Lateral to the 

 commencement of the lacrimal canal is a shallow depression for the origin of 

 the inferior oblique. 



The nasal surface takes part in the formation of the lateral wall of the nasal 

 fossa. It presents a large irregular aperture which leads into the antrum and, 

 immediately in front of this, the lacrimal groove, cUrected downward, backward, 

 and laterally into the inferior meatus of the nose. The groove is converted 



