THE LACRIMAL 85 



and is overhung by the maxillary process. The medial surface is convex, pitted 

 with depressions, and grooved for vessels, which, for the most part, run longi- 

 tudinally. The superior or attached border articulates in front with the conchal 

 crest of the maxilla, then ascends to form the lacrimal process, w^hich articulates 

 with the lacrimal bone and forms part of the wall of the lacrimal canal. Behind 

 this, it is turned downward to form the maxillary process, already mentioned, 

 which overhangs the orifice of the maxillary sinus and serves to fix the bone firmly 

 to the lateral w^all of the nasal fossa. The projection behind the maxillary process 

 is the ethmoidal process, joined in the articulated skull with the uncinate process 

 of the ethmoid across the opening of the maxillary sinus. Posteriorly the upper 

 border articulates with the conchal crest of the palate. The inferior border 

 is free, rounded, and somewhat thickened. The anterior extremity is blunt and 

 flattened, and broader than the posterior extremity, which is elongated, narrow, 

 and pointed. 



Articulations. — -With the maxilla, lacrimal, palate, and ethmoid. 



Ossification. — The inferior nasal concha is ossified in cartilage from a single nucleus which 

 appears in the fifth month of intra-uterine life. At birth it is a relatively large bone and fiUa 

 up the lower part of the nasal fossa. 



THE LACRIMAL 



The lacrimal bone [os lacrimale] (fig. 105) is extremely thin and delicate, 

 quadrilateral in shape, and situated at the anterior part of the medial wall of the 

 orbit. It is the smallest of the facial bones. 



The orbital surface is divided by a vertical ridge, the posterior lacrimal 

 crest, into two unequal portions. The anterior, smaller portion is deeply grooved 

 to form the lacrimal groove, which lodges the lacrimal sac and forms the com- 

 mencement of the canal for the naso-lacrimal duct. The portion behind the 

 ridge is smooth, and forms part of the medial wall of the orbit. The ridge gives 

 origin to the orbicularis oculi (pars lacrimalis) muscle and ends below in a hook-like 

 process, the lacrimal hamulus, which curves forward to articulate with the lacrimal 

 tubercle of the maxilla and completes the superior orifice of the naso-lacrimal 

 canal. The medial surface is in relation with the two anterior cells of the ethmoid 

 (lacrimo-ethmoidal), forms part of the infundibulum, and inferiorly looks into 

 the middle meatus of the nose. The superior border is short, and articulates 

 with the medial angular process of the frontal. The inferior border posterior to 

 the crest joins the medial edge of the orbital plate of the maxilla. The narrow 

 piece, anterior to the ridge, is prolonged downward as the descending process 

 to join the lacrimal process of the inferior nasal concha. The anterior border 

 articulates with the posterior border of the frontal process of the maxilla and the 

 posterior border with the lamina papyracea of the ethmoid. 



The vessels of the lacrimal bone are derived from the infra-orbital, dorsal nasal branch of 

 the ophthalmic, and anterior ethmoidal arteries. 



Articulations. — The lacrimal articulates with the ethmoid, maxilla, frontal, and inferior 

 nasal concha. 



Ossification. — This bone arises in the membrane overlying the cartilage of the fronto-nasal 

 plate, and in its mode of ossification is very variable. As a rule, it is formed from a single 

 nucleus which appears in the third or fourth month of intra-uterine life. Not infrequently, the 

 hamulus is a separate element, and occasionally the bone is divided by a horizontal cleft, a pro- 

 cess of the lamina papyracea projecting between the two halves to join the frontal process of 

 the maxilla. More rarely the bone is represented by a group of detached ossicles resembling 

 Wormian bones. 



The hamular process is regarded as representing the remains of the facial part of the 

 lacrimal seen in lower animals. 



THE VOMER 



The vomer (fig. 106) (ploughshare bone) is an unpaired flat bone, which lies 

 in the median plane and forms the lower part of the nasal septum. It is thin and 

 irregularly quadrilateral in form, and is usually bent somewhat to one side, 

 though the deflection rarely involves the posterior margin. Each lateral surface 

 is covered in the recent state by the mucous membrane of the nasal cavity, and is 

 traversed by a narrow but well-marked groove, which lodges the naso-palatine 

 nerve from the spheno-palatine ganghon. 



