THE NASAL BONES 99 



a thin transverse bony partition into two sets, which do not communicate with 

 each other; they are termed the anterior and posterior ethmoidal sinuses. The former, 

 more numerous, communicate with the frontal sinuses above and the middle 

 meatus below by means of the infundibulum; the posterior, less numerous, open 

 into the superior meatus and communicate (occasionally) with the sphenoidal 

 sinuses. In some cases the ethmoidal sinuses communicate with the maxillary 

 sinus. In some cases the os planum never develops, and the ethmoidal sinuses 

 are separated from the orbit merely by membrane. 



Development. The ethmoid is developed in cartilage from three centres one for the per- 

 pendicular lamella, and one for each lateral mass. The lateral masses are first developed, 

 ossific granules making their appearance in the os planum between the fourth and fifth months 

 of fetal life, and extending into the turbinated processes. At birth the bone consists of the two 

 lateral masses, which are small and poorly developed. During the first year after birth the 

 perpendicular plate and crista, galli begin to ossify, from a single centre, and become joined to the 

 lateral masses about the beginning of the second year. The cribriform plate is ossified partly 

 from the perpendicular plate and partly from the lateral masses. The formation of the ethmoidal 

 cells, which completes the bone, does not commence until the end of the fourth year. 



Articulations. With thirteen bones the sphenoid, the frontal, and eleven of the face, the 

 two nasal, two palate, two maxillae, two lacrimal, two turbinated, and the vomer. No muscles 

 are attached to this bone. 



THE BONES OP THE FACE (OSSA FACIEI). 



The facial bones are fourteen in number viz., the 



Two nasal. Two palate. 



Two maxilla?. Tw r o turbinated. 



Two lacrimal. Vomer. 



Two malar. Mandible. 



The Nasal Bones (Ossa Nasalia). 



The nasal bones are two small oblong bones, varying in size and form in dif- 

 ferent individuals; they are placed side by side at the middle and upper part of 

 the face, forming by their junction "the bridge" of the nose (Fig. 67). Each 

 bone presents for examination two surfaces and four borders. 



Surfaces. The outer surface is concave from above downward, convex from 

 side to side; it is covered by the Pyramidalis and Compressor nasi muscles. It 

 is marked by numerous small arterial furrows, and perforated about its centre 

 by a foramen (foramen nasale), sometimes double, for the transmission of a 

 small vein. 



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

 in which direction it is traversed by a longitudinal groove (sometimes a canal), 

 for the passage of a branch of the nasal nerve. 



Borders. The superior border is narrow, thick, and serrated, for articulation 

 with the nasal notch of the frontal bone. 



The inferior border is broad, thin, sharp, inclined obliquely downward, out- 

 ward, and backward, and serves for the attachment of the lateral cartilage of 

 the nose. This border presents, about its middle, a notch, through which passes 

 the branch of the nasal nerve above referred to, and is prolonged at its inner 

 extremity into a sharp spine, wjiieh, when, articulated with the opposite bone, 

 forms the nasal angle. < . , , . \ 



