THE SENSE OF SMELL. 



821 



bristles vibrated, being adapted for special tones. In cephalopoda, we distinguish the first 

 differentiation into a membranous and cartilaginous labyrinth. 



Historical. Empedocles (473 B.C.) referred auditory impressions to the cochlea. The 

 Hippocratic School was acquainted with the tympanum, and Aristotle (384 B.C.) with the 

 Eustachian tube. Vesalius (1561) described the tensor tympani ; Cardanus (1560) the conduc- 

 tion through the bones of the head ; while Fallopius (1561) described the vestibule, the semi- 

 circular canals, chorda tympani, the two fenestra?, the cochlea, and the aqueduct. Eustachius 

 (t 1570) described the modiolus, the lamina spiralis of the cochlea, the Eustachian tube, as 

 well as the muscles of the ear ; Plater the ampullae (1583) ; Casseri (1600) the lamina spiralis 

 membranacea. Sylvius (1667) discovered the ossicle called by his name ; Vesling (1641) the 

 stapedius. Mersenne (1618) was acquainted with overtones ; Gassendus (1658) experimented 

 on the conduction of sound. Acoustics were greatly advanced by the work of Chladni (1802). 

 The most recent and largest work on the ear in vertebrates is by G. Retzius (1881-84). 



The Sense of Smell. 



420. STRUCTURE OF THE ORGAN OF SMELL. Regio Olfactoria. The area of the 

 distribution of the olfactory nerve is the regio olfactoria, which embraces the upper part of the 

 septum, the upper, and part of the middle (Cm) turbinated bone (fig. 601, Cs). All the 

 remainder of the nasal cavity is called the regio respiratoria. These two regions are distin- 

 guished as follows : (1) The regio olfactoria has a thicker mucous membrane. (2) It is covered 

 by a single layer of cylindrical epithelium, the cells being often branched at their lower ends, 

 and contain a yellow or brownish-red pigment (figs. 602, 603, E). (3) It is coloured by this 

 pigment, and is thereby distinguished from the uncoloured regio respiratoria, which is covered 



Epithe- 

 lium. ( 



Mucous 

 Mem- / 

 brane, 



Fig. 601. 



Fig. 601. Nasal and pharyngo-nasal cavities. L, levator elevation ; P.s.p., plica salphingo- 

 palatina ; Cs, Cm, Ci, the three turbinated bones (Urbantschitsch). Fig. 602. Vertical 

 section of the olfactory region (rabbit), x 560. s, disc ; zo, zone of oval, and zr of spherical 

 nuclei ; b, basal cells ; dr, part of a Bowman's gland ; n, branch of the olfactory nerve. 



by ciliated epithelium. (4) It contains peculiar tubular glands (Bowman's glands), described 

 as "mixed glands " by Paulsen ( 142), while the rest of the mucous membrane contains numer- 

 ous acinous serous glands (Heidenhain) ; but in man the latter are said to be mixed glands 

 (Stbhr) (fig. 602). Lymph-follicles lie in the mucous membrane, and from them numerous 

 leucocytes pass out on to free surface (Stohr). (5) Lastly, the regio olfactoria embraces the 



