ORGANS OF SENSE. 153 
h—k, second branch. Figs. 41 and 42, two sections of the nasal cavities : 
fig. 41, the lower, fig. 42, the upper: a, outline of the nose; 0, c, nasal 
bones; d, e, frontal bone; fg, 2, 7, ethmoid bones; g, ?, &, J, alar process and 
sphenoid bone (cut edge); 7, 7, middle lamina of the ethmoid bone (cut edge); 
s, s, and ¢, ¢, thickness of the mucous membrane of the nose; w, u, length and 
breadth of the left, v, v, of the right nasal cavity; w, w, x, x, cells of the 
ethmoid bone; y, z, membrane reflexed. /%y. 48, posterior surface of a 
vertical section of the nose; a, 0, nasal cartilages; c¢, c, septal cartilage ; 
d, d, Schneiderian membrane; e, ¢, hairs and mucous glands; /; g, nostrils. 
Fig. 44, posterior sectional surface of the nasal cavities: a—/, cut edge of 
various bones; g, , lachrymal sac and lachrymal duct opening*into the 
inferior meatus; 2, k, /, m, section of the Schneiderian membrane; n, n, the 
surface of the membrane turned towards the nasal cavity; p, g, lachrymal 
sac and lachrymal duct of the left side; 7, 7, inner bony wall of the maxil- 
lary sinus. /%g. 45, posterior sectional surface of the nasal cavities and 
the communicating sinuses: a, 5, frontal bone; c—/, ethmoidal; m, n, left 
and right superior turbinated bones; p, p, vomer; g—y, upper jaw; a, ff 
Schneiderian membrane ; g, g, opening of the left lachrymal canal ; h, open- 
ing of the right; k, 1, m, opening of the maxillary sinus on the right side, 
m is a probe introduced; n, 0, p, section of the periosteum of the orbit; s, 
section of the soft palate; *°, teeth. 
38. ANATOMY OF THE HAR, OR ORGAN OF HEARING 
By means of the sense of hearing an animal is enabled to take cognisance 
of sounds and of all their variations. Sound is the result of any impulse 
conveyed to the organs of hearing, by undulations of air, these organs being 
so constructed as to receive these undulations, and so organized as to become 
sensible to them and to convey the impressions to the sensorium. This 
sense, next to vision, is most valuable to man, as forming the bond of social 
union and the great inlet for all knowledge conveyed by voice and language. 
Each organ consists of a special nerve expanded on membranes, and en- 
dowed with the properties of sensibility to the varying impressions of sound 
and of conveying these impressions to the sensorium; and secondly, of a 
physical apparatus fitted for receiving, conducting, and in some measure 
regulating these impulses in their course to the sentient nerve. 
We may divide the ear into an external, middle, and internal portion. 
The external comprises the auricle, commonly called ear, and the external 
meatus or tube; the middle consists of the tympanum or drum with its 
chain of small bones; and the internal or true ear is called the labyrinth, 
and comprises the vestibule, cochlea, semicircular canals, meatus auditorius 
internus, and auditory nerve. This portion is lodged in the petrous divi- 
sion of the temporal bone, and is thereby protected from external pressure 
or injury. 
