86 



THE SKELETON 



The superior border, bj^ far the thickest part of the bone, is expanded laterally 

 into two alse. The groove between them receives the rostrum of the sphenoid, 

 and the margin of each ala comes into contact with the sphenoidal process of the 

 palate and the vaginal process of the medial pterygoid plate. The inferior border 

 is uneven and lies in the groove formed by the crests of the maxillary and palate 

 bones of the two sides. The anterior border slopes downward and forward and is 

 grooved below for the septal cartilage of the nose; above it is united with the 

 perpendicular plate of the ethmoid. The posterior border, smooth, rounded, and 

 covered by mucus membrane, separates the posterior nares. The anterior and 

 inferior borders meet at the anterior extremity of the bone which forms a short 

 vertical ridge behind the incisor crest of the maxillse. From near the anterior 

 extremity, a small projection passes downward between the incisive foramina. 



Fig. 106. — The Vomer. (Side view.) 



Anterior border 



Groove for naso-palatine nerve 

 Groove for septal cartilage 



Inferior border — 



Ala 



Posterior border 



Blood-supply.— The arterial supply of the vomer is derived from the anterior and posterior 

 ethmoidal and the spheno-palatine arteries. Branches are also derived from the posterior 

 palatine through the foramen incisivum. 



Ossification. — The vomer is ossified from two centres which appear about the eighth week 

 in the membrane investing the ethmo-vomerine cartilage. The two lamella; unite below during 

 the third month and form a shallow bony trough in which the cartilage lies. In the process 

 of growth the lamellae extend upward and forward and gradually fuse to form a rectangular 

 plate of bone, the cartilage enclosed between them undergoing absorption at the same time. 

 The alse on the superior margin and the groove in front are evidence of the original bilaminar 

 condition. 



THE NASAL 



The nasal (figs. 107 and 108) are two small oblong bones situated at the upper 

 part of the face and forming the bridge of the nose. Each bone is thicker and 

 narrower above, thinner and broader below, and presents for examination two 

 surfaces and four borders. 



Fiu. 107. — The Left Nasal Bone, 

 Facial Surface. 



Superior border 



Medial border 

 Lateral border 



Inferior border' 



Fig. 108. — The Left Nasal Bone, 

 Nasal Surface. 



Medial border 



Groove for external nasal branch of 

 anterior ethmoidal nerve 



The facial surface is concave from above downward, convex from side to side, 

 and near the centre is perforated by a small foramen, which transmits a small 

 tributary to the facial vein. The posterior or nasal surface, covered in the recent 

 state by mucous membrane, is concave laterally, and traversed by a longitudinal 

 groove [sulcus ethnioidalis] for the anterior ethmoidal branch of the ophthalmic 

 division of the fifth nerve. The short superior border is thick and serrated for 

 articulation with the medial part of the nasal notch of the frontal. The inferior 

 border is thin, and serves for the attachment of the lateral nasal cartilage. It 

 is notciied for the external nasal branch of the anterior ethmoidal nerve. The 

 nasal bones of the two sirles are united by their medial borders, forming the inter- 

 nasal suture. The contiguous borders ar(! ])r()longed backward to form a crest 

 which rests on the frontal spine and tiu! anterior border of the perpendicular 

 plate of the ethmoid. Tiie lateral border articulates with the frontal process 

 of the maxilla. 



