144 



OSTEOLOGY. 



cellular above ; it closes in some of the anterior ethmoidal cells and helps to 

 complete the infundibulum. Where it is smoother it forms a part of the 

 lateral wall of the middle meatus of the nose immediately behind the frontal 

 process of the maxilla, and above the inferior concha. The superior border 

 articulates with the orbital part of the frontal; the anterior edge with the 

 posterior border of the frontal process of the maxilla, with which it completes 

 the lacrimal groove for the lodgment of the lacrimal sac. The inferior margin 

 articulates with the orbital surface of the maxilla, and in front by its descending 

 process with the inferior concha. Posteriorly the bone articulates with the 

 anterior border of the lamina papyracea of the ethmoid. 



Connexions. The lacrimal bone articulates with fou-r bones the frontal, ethmoid, inferior 

 concha, and the maxilla. 



Ossification. The lacrimal is developed from a single centre, which makes its 

 appearance about the end of the second or the beginning of the third month of intra- 

 uterine life in the membrane around the cartilaginous nasal capsule. 



Palate 



Maxilla 



FlG. 154. TflE VOMER AS SEEN FROM THE 



RIGHT SIDE. 



Vomer. 



The vomer or ploughshare bone, a bone of irregular quadrilateral shape, is 

 placed in the posterior part of the nasal septum. It has four borders and two 



surfaces. The superior border, which can 

 Groove for readily be distinguished by the presence 



ias ne?ve tm Groove on either side of an everted lip or ala, 

 WL> / ^JJ 3 ?!^ 1 s ^P es from behind upwards and forwards, 



and articulates with the inferior surface 

 of the body of thfe sphenoid, the pointed 

 rostrum of which is received into the 

 groove bounded by the projecting alae. 

 Laterally these alas are wedged in between 

 the sphenoidal processes of the palate 

 bones in front, and the vaginal processes 

 at the root of the medial laminae of the 

 pterygoid processes behind. The posterior border, which slopes from behind down- 

 wards and forwards, is free, and forms a sharp, slightly curved edge; this con- 

 stitutes the posterior margin of the nasal septum, and 

 serves to separate the openings of the choanae (O.T. 

 posterior nares). The inferior border, more or less 

 horizontal in direction, articulates with the nasal 

 crest formed by the maxillae and palate bones. The 

 anterior edge is the longest ; it slopes obliquely from _ 



-, -, j j ^ j T j i i r Vomer at Birth, displaying its forma- 



above downwards and forwards. In its upper half ti0 n by two Osseous Lamime united 

 it is ankylosed to the perpendicular plate of the inferioriy. The figure to the right 

 ethmoid ; in its lower half this margin is grooved for exhibits the appearance of the bone, 

 the reception of the septai cartikge of the nose. L"int?^^ ^ 

 The anterior extremity of the bone forms a trun- 

 cated angle, which articulates with the posterior border of the incisor crest of 

 the maxillae, and sends downwards a pointed process which passes between 

 the incisor foramina. The right and left surfaces of the bone are smooth and 

 covered by mucous membrane. It is not uncommon to find them deflected to 

 one or other side. A few vascular grooves may be noticed scattered over these 

 surfaces, and one, usually more distinct than the others, running obliquely down- 

 wards and forwards, indicates the course of the naso-palatine nerve. 



Connexions. The vomer articulates with the sphenoid, the ethmoid, the palates, and the 

 maxillae. In front it supports the septai cartilage. 



Ossification. The vomer commences to ossify in membrane at the end of the 

 second month. A nucleus appears on each side of the middle line, below the nasal 

 septum, medial to the plane of the anterior paraseptal cartilages and posterior to them. 

 During the third month the nuclei, which have increased in height and length, 



FIG. 155. 





