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). ddie partition between the fossae 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 1 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 
t f o n m 
Fig. 221. —Skull op Horse. 
cc, occipital bone ; t, temporal ; /, frontal ; n, nasal; m, superior maxillary ; im, 
intermaxillary; mi, inferior maxillary; o, orbit; i, 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, cribrum, a sieve. 
H H 2 
