BONES OF THE FACE. 467 



as the back of the mouth, and communicates with the 

 pharynx by two apertures termed the posterior nares (fig. 

 200, c). The partition between the fossse is formed at the 

 upper part by a plate that projects downwards from the eth- 

 moid bone, and at the lower by a distinct bone called the 

 vomer (or ploughshare) from its peculiar form ; to the front 

 edge of this last is attached a cartilage, which continues the 

 partition forwards into the soft projecting portion of the nose. 

 It is through the thin horizontal plate of the ethmoid bone, 

 which separates the nasal cavity from that of the skull, that 

 the olfactory nerves make their way out from the former into 

 the latter : they descend in numerous branches, for the passage 

 of which through the roof of the nose this plate is perforated 

 by a number of small apertures, which give it a sieve-like 

 aspect; whence it is called the cribriform^- plate of the 

 ethmoid. 



623. It is in the superior maxillary bone that all the teeth 

 of the upper jaw are implanted in Man ; but in the embryo 

 this bone is composed of several pieces ; and one of these 

 pieces, termed the intermaxillary bone (im, fig. 221), remains 



mi mo c 



Fig. 221. SKULL op HORSE. 



OC, occipital bone ; t, temporal ; /, frontal ; , nasal ; tn, superior maxillary ; im, 

 intermaxillary; mi, inferior maxillary; o, orbit; , incisor teeth; c, canines; mo, 

 molars. 



permanently separate in most of the lower animals. The 



lower jaw of adult Man, also, is composed but of a single 



piece ; though this is divided in the infant on the central line, 



and the two halves remain separate in many of the lower 



animals. This bone has a general resemblance in form to a 



horse-shoe with its extremities turned up considerably ; it is 



1 From the Latin, crilrum, a sieve. 



H H 2 



