OSTEOLOGY. 39 



surmounted by the middle portion of the zygomatic ridge, 

 to which masseter externus is attached. The superior 

 surface is concave, occupies the centre of the bone, being 

 continued neither to the superior extremity nor to the 

 inferior, and assists in foruiing the orbit. The internal 

 surface is concave, and wholly occupied by a squamous 

 surface ; the major portion lies in apposition with the 

 superior maxillary bone, but at the antero-superior angle it 

 unites with the lachrymal bone. The base, external and 

 internal margins are the sharpened edges of the squamous 

 surface. The superior margin anteriorly is serrated for 

 union with os lachrymale, centrally smooth, rounded, and 

 concave, forming the outer margin of the orbit ; pos- 

 teriorly it is continuous at the apex on to the superior 

 surface, forming a squamous facet for the antero-external 

 part of the zygomatic process of the squamous temporal 

 bone. 



The VOMER, so named from the resemblance of the 

 corresponding bone in man to a ploughshare, is the only 

 single bone in the facial portion of the upper jaw. 

 It presents two margins, two extremities, and two surfaces. 

 This bone posteriorly forms the line of division of the 

 posterior nares ; anteriorly it is continued almost as far as 

 the anterior naris on the floor of the nasal cavity between 

 the two chambers. Its inferior border anteriorly presents 

 a roughened articulatory surface, which fits into a groove 

 formed by the junction of the palatine processes of the 

 superior and anterior maxillae of one side with the corre- 

 sponding parts of the other, being an example of the form 

 of joint known as schindylesis. The posterior part of th^ 

 inferior border is covered by mucous membrane ; centrally 

 it is sharp, dividing the posterior nares, posteriorly expands, 

 terminating on either side in a sharp point, which is con- 

 cealed by the pterygoid bone. The superior margin con- 

 sists of two thin plates of bone passing upwards one on 

 each side to form a groove into which septum nasi fits. 

 These plates gradually increase in length (and the groove 

 accordingly in depth) from before backwards to about the 

 anterior part of the posterior third of the bone, where they 

 become widened, presenting on their external surfaces 

 concave squamous articulations for the inner ridges of the 

 palatine bones. At the extreme posterior part they meet 

 the under surface of the ethmoid and sometimes extend as 



