THE BONES OF THE HEAD 



"5 



Anterior Border 



Groove for Naso-palatine Nerve 



Inferior Border 



forwards, and it may present two alae, but these are very thin, 

 and lie near each other, being separated by a narrow cleft. These 

 characters are always more pronounced in earlier life. The cleft 

 in its lower part receives the septal nasal cartilage, and superiorly 

 the perpendicular plate of the ethmoid fits into it, being usually 

 ankylosed with one or both alae. In many cases, however, the 

 anterior border is simply grooved. The posterior border is sharp, 

 and almost vertical, and lies between the posterior nares. The 

 anterior extremity forms a short irregular lip, which touches the 

 back parts of the incisor crests of the superior maxillae. 



The bone receives its blood-supply from the spheno-palatine 

 branch of the in- 

 ternal maxillary Superio^r Border 



artery. 

 Articulations. 



— The vomer ar- 

 ticulates with six 

 bones, as follows : 

 the sphenoid, two 



palate bones, eth- Posterior Border 



moid, and superior 

 maxiUae. In addi- 

 tion to these, it 

 articulates with the 

 septal nasal carti- 

 lage. 



Structure. — ^The vomer is composed of two thin pkites of compact 

 bone, which are blended into one, except superiorly, and, it may be, 

 to a certain extent anteriorly. 



Varieties. — The bone is often much deflected to one or other side, more 

 frequently the left, and so it may curtail the cavity of the nasal fossa to 

 which it is deflected. 



Ossifieation. — The vomer is developed in membrane from two centres, which 

 appear about the eighth week of intra-uterine hfe. The centres unite below 

 in the third month, and form a groove in which the septal nasal cartilage lies. 

 The laminae forming the lips of the groove continue to grow upwards and 

 forwards, and subsequently fuse, the enclosed cartilage becoming absorbed. 

 Ultimately there are left the alae on the superior border, and, it may be, on the 

 anterior border, which are permanent indications of the original bilaminar 

 condition of the bone. 



The Inferior Maxillary Bone. 



The inferior maxillary bone or mandible supports the lower teeth, 

 and articulates at either side with the anterior part of the glenoid 

 fossa of the temporal in a freely movable manner. It has the 

 shape of a horse-shoe, and consists of a central horizontal portion, 

 called the body, and two upright portions, called the rami. 



The body is arched, being convex in front and concave behind, 

 and it presents two surfaces and two borders. The external surface 

 presents a slight median vertical ridge over its upper two-thirds, 

 which marks the symphysis or place of union of the two halves 



Fig. 71. — The Vomer (Lateral View). 



