THE LACHRYMAL BONE. 



57 



end. The external border is the longest, and articulates with the nasal process of 

 the superior maxilla, being supported by small teeth which fit into depressions on 

 the edge of that bone. The internal border is thicker above than below, and meets 

 its fellow in the somewhat irregular internasal suture, which commonly deviates to 

 one side at the upper end : the two 

 bones form posteriorly a median crest, 

 which rests from above down upon the 

 nasal spine of the frontal bone, the ver- 

 tical plate of the ethmoid (fig. 66), and 

 the septal cartilage of the nose. The 

 anterior or facial surface is concave from 

 above down at its upper part, convex 

 below, and presents a small vascular fora- 

 men. The posterior or nasal surface is 

 rough for a short distance above, where it 



Fig. 58. RIGHT NASAL BONE : A, INNER VIEW ; 

 B, OUTER VIEW. (Drawn by D. Gunn.) 



rests upon the nasal process of the frontal 



bone (fig. 38) ; in the rest of its extent it 



is concave and smooth, being lined by the 



mucous membrane of the nose ; and a little external to its centre it is traversed by 



a small longitudinal groove which lodges the nasal nerve. 



Varieties. The form and dimensions of the nasal bones vary greatly in different indi- 

 viduals. They are in general relatively large and prominent in the white races, small and 

 flat in the dark and yellow races. Fusion of the two bones, by obliteration of the internasal 

 suture, is occasionally, though rarely, met with : this condition is usual in apes. 



THE LACHRYMAL BONE. 



The lachrymal bone, or os vnguis, is a thin scale of bone placed at the 

 anterior and inner part of the orbit (fig. 69). It articulates above with the frontal 

 bone, behind with the orbital plate of the ethmoid, 

 and in front with the nasal process of the superior 

 maxilla. 



The external surface is divided by a vertical ridge, 

 the lachrymal crest, into two parts : the anterior is 

 grooved, lachrymal groove, for the lachrymal sac, and 

 this part is prolonged inferiorly beyond the orbit as the 

 descending process which assists in bounding the canal 

 of the nasal duct, and articulates with the inferior 

 turbinate bone ; the posterior part, broader, is flat, con- 

 tinuous with the orbital surface of the ethmoid, and is 

 produced below into a hook-like projection, the hamular 

 process, which curves forwards in the lachrymal notch of 



the superior maxilla and bounds the orifice of the nasal duct on the outer side 

 (fig. 66). The internal surface superiorly completes some anterior ethmoidal cells, 

 and inferiorly looks into the middle meatus of the nose. 



Varieties. The lachrymal tone varies much in size : complete absence has been observed. 

 It is sometimes perforated, or reticulate, or divided into two or more pieces. The hamular 

 process is often very small, and sometimes wanting. On the other hand it may be unusually 

 long, and reach the orbital margin, or even, in rare cases, extend slightly onto the face : 

 this represents a more largely developed facial portion of the lachrymal bone in many 

 mammals. Occasionally the place of the hamular process is taken by a separate ossicle. 

 (Gegenbaur, Morph. Jahrb., vii. ; Macalister, Proc. Eoy. Soc., 1884.) 



Fig. 59. RIGHT LACHRYMAL 

 BONE: OUTER VIEW. (Drawn 

 by D. Gunn.) 



