THE LACEIMAL BONES. 143 



ij.t articulates with the inferior conchal crests on the medial surface of the body 

 inf the maxilla and the perpendicular part of the palate bone, respectively. Be- 

 tween these two articulations the central part of the superior border rises in the 



t'orm of a sharp crest, the anterior part of which forms the upstanding lacrimal 



process which articulates above with the descending process of the lacrimal bone, 



as well as with the edges of the naso-lacrimal groove of the maxilla, thus com- 

 pie ting the osseous canal of the naso-lacrimal duct. The posterior end of this crest 

 is elevated in the form of an irregular projection called the ethmoidal process. This 

 j unites with the uncinate process of the ethmoid bone (see Fig. 150). Spreading 



downwards from the middle of the superior border, on its lateral side, is a thin 

 'irregular plate of bone, the maxillary process, which partially conceals the lateral 

 iconcave surface of the bone, and, by its union with the medial wall of the 



maxillary sinus, assists in the completion of the partition which separates that 



cavity from the inferior nasal meatus. 



The inferior or free border, gently curved from before backwards and turned 



slightly laterally, is rounded and full, and formed of bone which is deeply pitted 

 land of a somewhat cellular character. The anterior and posterior extremities of 

 jthe bone, formed by the convergence of the superior and inferior borders, are thin 

 i and sharp ; as a rule the posterior end is the more pointed of the two. The medial 



surface projects into the nasal cavity ; convex from above downwards, and slightly 

 .curved from before backwards, it forms the floor of the middle meatus. It is 



rough and pitted, and displays some scattered and longitudinally directed vascular 



grooves. The lateral surface overhangs the inferior meatus of the nose. Concave 

 ;from above downwards, and to some extent from before backwards, it is directed 



towards the lateral wall of the nasal cavity. It is smooth in front, where it 

 .corresponds to the opening of the canal for the naso-lacrimal duct; behind and 

 1 towards its inferior border it is irregular and pitted. In the disarticulated bone 



this surface is in part concealed by the downward projecting maxillary process. 



Connexions. The inferior concha articulates with the maxilla, lacrimal, ethmoid, and 

 palate bones. 



Ossification. The inferior concha (the maxillo-turbinal of comparative anatomy) 

 is derived from the cartilage forming the lateral wall of the nasal capsule, the upper 

 portion of which forms the ethmo - turbinals. It ossifies, however, from a separate 

 (centre, which appears about the fifth month of foetal life, and later contracts a union 

 by a horizontal lamella on its lateral side with the maxilla. 



Ossa Lacrimal ia. 



The lacrimal bone, a thin scale of bone about the size of a finger-nail, forms part 

 of the medial orbital wall behind the frontal process of the maxilla. Irregularly 

 quadrangular, it has two surfaces a medial and lateral and four borders. 



Its lateral or orbital surface has a vertical ridge, the crista lacrimalis pos- 

 terior (posterior lacrimal crest), running downwards upon it. In front of this is 

 ithe sulcus lacrimalis (lacrimal groove) for the lodgment of the lacrimal sac. The 

 medial wall of this groove descends below the level of the 

 bulk of the bone, and forms the descending process, which orbital surface 

 helps to complete the osseous canal for the naso-lacrimal 

 duct, and articulates inferiorly with the inferior concha. 

 The inferior end of the lacrimal crest terminates in a hook- 

 like projection, the hamulus lacrimalis (lacrimal booklet), 

 which curves round the posterior and lateral edge of 

 ithe naso-lacrimal notch of the maxilla, and thus defines 

 the upper aperture of the canal for the naso-lacrimal duct. 

 To the free edge of the crest, behind the lacrimal groove, are 

 attached the reflected portion of the medial palpebral liga- FlG i53._R IGHT LACRIMAL 

 ment and the lacrimal part of the orbicularis oculi, the crest BONE (Orbital Surface), 

 being sometimes thickened at the site of this attachment. 



The part of the bone behind the lacrimal crest is smooth and continuous with the 

 \ surface of the lamina papyracea of the ethmoid. The medial surface is irregular and 



