356 AVERS. 



EXPLANATION OF PLATE X. 



Fig. I. A preparation of the organ of Corti of the Virginia Opossum in osmic 

 acid, to demonstrate the course of the nerves across the arch of Corti. g., gangli- 

 onic ( ?) varicosity of the nerve fibres, n. c.p.f., foot of Corti's pillar, nl.cp., nu- 

 cleus of the pillar cell of the outer pillars. /., projection from the apex of the arch. 

 X865. 



Fig. 2. A view of the internal ear oi Petromyzon marinus, from above and with- 

 out, to show the relation of the sense organ to the commissural chamber and the 

 manner in which the two endolymphatic tubes pierce the walls of the utriculus and 

 sacculus respectively, v., v.', the utricular and saccular chambers, c.a. and c.p., the 

 anterior and posterior semicircular canals, s.o., sense organ of the commissure. 

 c, commissural chamber, in which it lies, d.e.s., ductus endolymphaticus utriculi. 

 d.e.u., ductus endolymphaticus sacculi. Owing to an inadvertence the d.e.s. of the 

 figure was placed on the sacculus. It should occupy a corresponding place on the 

 utriculus. m.r., median raphe, but partly separating the two chambers of the ear. 

 VIII ac, the auditory accessory nerve which supplies the commissural and surface 

 canal sense organs. X 20. 



Fig. 3. Transverse section of the cochlear organ of the Alligator (^A. mississip- 

 piensis), to show the relation of the parts, c.n.f., cochlear nerve fibres, c.n.g., 

 cochlear nerve ganglion cells, c.c.', cartilaginous bars framing the membrana basi- 

 laris. l.e.r. and s.e.r., large and small epithelial ridges of the Alligator ear 

 e.eJ, two apparently non-hair-bearing epithelial ridges, b.v., blood-vessels, s.t., 

 scala tympani. s.v., scala vestibuli. c.c, cochlear canal, h.b., hair band. sir. v., 

 stria vascularis, a.h., auditory hairs, r.p.b,, ramulus papillae basilaris n. cochleae. 

 V.S., spiral vessels, c.a., cochlear artery, sh., sheath of cochlear nerve. X 30. 



Fig. 4. A small portion of the preceding figure more highly magnified, to show 

 the hair band and its composition and relation to the short hairs still connected with 

 the sensory cells. a.h., auditory hairs, h.c, hair cells, sp.c, supporting cells. 

 h.b., hair band. ahJ and ahJ\ the free ends of the auditory hairs projecting beyond 

 the bounds of the hair band or membrana tectoria, which has been torn from its 

 attachment to the hair cells. «., nerve fibres, b.m., basilar membrane. 



Fig. 5. A horizontal section of the sense organ of the commissure from the Petro- 

 myzon ear. s.t., supporting stalk of the sense organ, h.c, hair cell, e.p., non-sensory 

 epithelium, b.t., basement tissue of the head of the organ, ct., connective tissue 

 of its stalk. X 380. 



Fig. 6. The figure represents the tortuous course of the non-medullate fibres (at 

 least, as seen in preparations) of the cochlear nerve across the interspace between 

 the habenula perforata and the hair cells. From the Pig. X 1065. 



Fig. 7. Surface view of the epithelium of Reissner's membrane in the Pig. The 

 nuclei of the middle layer of cells shows through the outlines of the inner layer, 

 X 440. Methyl blue. 



