THE MAXILLA 56 



prolonged luu-kAvards to form a crot; this crest comes into relation with the nasal 

 spine of the frontal and the anterior border of the mesethmoid. The outer border 

 articulates witli the nasal process of the maxilla. 



Articulations. — The nasal bone articulates witli its fellow, the frontal, maxilla. 

 and ethmoid. 



Blood-supply. — Twigs to this bone are furnished by the nasal branch of the 

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



Ossification. — Each nasal bone is developed from a single earthy nucleus in the 

 membrane overlying the fronto-nasal cartilage. The nucleus is easily seen during 

 the eighth week. The bone by its pressure soon produces aV)sorption of the under- 

 lying cartilage. At l)irth the nasal bones are nearly as wide as they are long, 

 whereas in the adult, the length of the bones is three times greater than the width. 



THE MAXILLA 



The maxilla^ are two hollow irregular cuboidal bones with two prominent pro- 

 cesses. They form a large portion of the facial skeleton. 



This bone is occupied by a large cavity, the antrum. The body presents four 

 surfaces. Of these the facial surface looks forwards and outwards and presents 

 the following points of interest: — The socket for the canine tooth causes a low 

 elevation, the canine eminence, having to its inner side the incisive fossa, from 

 Avhieli the depressor ahe nasi arises. On the outer side of the eminence is the 

 canine fossa, which gives origin to the levator anguli oris. Above this fossa is the 

 infraorbital foramen, through which the terminal Vjranches of the infraorbital 

 nei-ve and artery emerge. From the ridge al)Ove this foramen the levator lahii siqx- 

 rioris arises. 



A ridge of bone extending upwards from the socket of the second molar tooth 

 separates the facial from the zygomatic surface. Near the middle of the zygo- 

 matic surface are the orifices of the canals for the posterior dental ner^-es and 

 vessels. The posterior inferior angle of this surface is termed the tuberosity ; from 

 it a few fibres of the internal pteri/(/oid nniscle arise. This tuberosity is most promi- 

 nent after eruption of the wisdom tooth; the rough surface along its inner border is 

 for the tuberosity of the palate bone; the smooth surface immediately above forms 

 the anterior boundary of the spheno-maxillary fossa, and enters into the formation 

 of the descending palatine canal. 



The orbital surface is irregularly triangular and forms the greater part of the 

 floor of the orbit. Anteriorly it is rounded and forms part of the circumference 

 of the orbit; externally it is rough for suture with the malar bone; the rough 

 surface ends in a backwardly projecting spine which occasionally joins the sphenoid 

 and forms the anterior limit of the spheno-maxillary fissure. The posterior 

 margin, smooth and rounded, forms the inferior limit of the spheno-maxillary 

 Assure. The internal border is nearly straight; quite at the posterior part is a 

 gap for the orlntal process of the palate bone; anteriorly it articulates with the 

 OS i)lanum of the ethmoid; beyond this it receives the lachrymal bone, and in the 

 anterior angle it is smooth and rounded, forming part of the circumference of the 

 orbital orifice of the lachrymal duct. 



The orbital surface is traversed b}' the infraorbital groove, which, commenc- 

 ing at the posterior border, deepens as it passes forwards and enters the infra- 

 orbital canal. This groove receives the second division of the fifth nerve and the 

 infraorbital artery. The infraorbital canal runs under the margin of the orbit 

 and opens on the facial surface. It transmits the infraorbital artery and nerve. 

 At the termination of the groove a smaller canal tunnels the anterior wall of tlie 

 antrum, and conveys the anterior dental nerves and vessels to the upper incisor, 

 canine, and l)icuspid teeth. External to the commencement of the lachrymal duct 

 there is a shallow depression frcmi which the inferior oblique takes origin. 



The internal or nasal surface forms the outer wall of the nasal fossa, and is 

 prolonged inwards to form ])art of the floor of this fossa. The posterior half of this 

 surface is deficient, and leads by a large irregular aperture into the antrum ; below 

 and behind this opening the bone is rough for articulation with the vertical plate 



