THE LACHRYMAL BONE. 



207 



THE LACHRYMAL BONE. 



The lachrymal bone ' is an exceedingly thin osseous plate, filling the vacancy in 

 the inner wall of the orbit between the orbital plate of the ethmoid and the ascending 

 process of the superior maxilla. It is quadrilateral, the long diameter being vertical, 

 and presents an outer surface directed towards the orbit and an inner surface towards 

 the nasal fossa. The latter rests, in part, against the turbinate process of the eth- 

 moid, which more or less overlaps it. It closes the infundibulum and several anterior 



Fig. 234. 



Orbital surface 



Lachrymal crest 



Nasal process of sup. max. 

 Lachrymal groove 



Hamular process 



Right lachrymal bone in place, outer aspect. 



Fig 



ethmoidal cells. The lower and anterior portion of this surface forms a part of the 

 wall of the middle nasal meatus. The outer surface is subdivided by a vertical ridge, ^ 

 marking off a smaller anterior part, which forms the iachryfual groove ;^ and, joining 

 the corresponding groove of the superior maxillary, complete the lachrymal canal. 

 The posterior part of the orbital surface is plane. The hamular 

 process * is a small tongue of bone curving forward from the lower 

 part of the dividing ridge to form the posterior border of the 

 canal at the floor of the orbit. The descending p7'ocess is a 

 downward prolongation of the grooved portion, forming part of 

 the wall of the canal, and meeting the lachrymal process of the 

 inferior turbinate. The bone also articulates with the frontal by 

 its upper surface, and with the front of the os planum by its pos- 

 terior border. 



Articulations. — The lachrymal articulates with the eth- 

 moid, frontal, superior maxillary, and inferior turbinate bones. 



Development. — Ossification is from a single centre said 

 to appear in the eighth foetal week, although the variations imply 

 extra ones. Macalister* enumerates six separate ossicles which 

 may occur about the bone. It varies greatly in size ; it may be wanting, though 

 rarely, and sometimes is very large. A considerable development of the hamular 

 portion, which may be separate, represents the condition of prosimians and platyrhine 

 apes.® It may be subdivided or perforated.' 



^ Proc. Royal Society, 18S4. 



^ Gegenbaur : Morph. Jahrbuch, Bd. vii. 



' Le Double : Essai sur la Morphogenie et les Variations du Lacrymal, 1900 ; and Zabel : 

 Varietaten und Vollstandiges Fehlen des Tranenbeins beim Menschen, Anat. Hefte. Bd. xv., 

 Heft I, 1900. 



^ Os lacrimale. - Crista lacrimalis. ' Sulcus lacrimalis. ■• Hamulus lacrimalis. 



Right lachrymal bons, 

 inner aspect. Upper 

 part completes anterior 

 ethmoidal cells, lower 

 looks into middle nasal 

 meatus. 



