342 AVERS, 



EXPLANATION OF PLATE III. 



Fig. I. A view in perspective of the developing organ of Corti of a Pig embryo 

 S\ inches in length. X 825. l.e.r., the large epithelial ridge and its hair cells. The 

 full complement of hairs to the cell is only indicated by the one hair, and only a small 

 number of the hairs are drawn, for the sake of clearness. The figure illustrates the 

 appearance of the organ during life, sat., the Sauropsid organ, s.e.r., small epithe- 

 lial ridge. The nerves and other parts are not indicated. For other detail of sec- 

 tion, see Fig. i, PI. VI, and Fig. 2, this plate. 



Fig. 2. A radial section of the cochlear canal and adjacent parts showing the 

 relation of the developing organ of Corti to the canal and to its nerve, s.e.r. and 

 l.e.r., small and large epithelial ridges respectively. The latter is the Sauropsid organ 

 which disappears by the time adult life is reached- Both organs are composed of 

 hair-bearing cells, which at this stage are very much alike, although the future organ 

 of Corti has begun its differentiation out of the small epithelial fold. 



Fig. 3. A fragment of a group of auditory hairs of the sensory hair band of the 

 organ of Corti of the Ox, isolated from the band, and partly teased out. X 850. 

 The figure illustrates the size and regularity of the capillary filaments, and the ab- 

 sence of an intermediate imbedding substance. 



Fig. 4. A view of the ventral surface of the hair band of the Ox, to illustrate the 

 manner in which the plate breaks away from the hair cells. The crenulate line cross- 

 ing the band from right to left is the inner half of the circular areas occupied by the 

 hairs after being torn off the cells. Osmic-glycerine preparation. X 44°. At ch.c. 

 the cap of one of the hair cells remains, and the hair ends may readily be counted. 



Fig. 5. Surface view of Loewenberg's net in its relation to the dorsal surface of 

 the sensory hair band of the Rabbit. X 180. The figure illustrates one extreme of 

 the complicated structures arising out of the destruction of the normal relation of the 

 surface layers of the hair band, i.k.b., inner border of the hair band, usually described 

 as composed of amorphous substance. 



Fig. 6. Transverse section of the cochlear canal of a 2^inch Pig embryo, to 

 show the epithelial ridge {l.e.r?), out of which the organ of Corti is developed, and 

 the other ridges, which for the most part disappear during later development in the 

 mammal. X about 350. 



Fig. 7. Side view of one rod of Corti of the Rabbit, showing the continuation of 

 the cell protoplasm up to the pillar head, and its penetration in between the spread- 

 ing fibres of the foot plate. The small figure at the side represents a cross-section 

 along the line " f," and shows that the bundle of fibres constituting the rod is inclosed 

 in the common sheath of the protoplasm. X 865. 



Fig. 8. A surface view of the outer end of an endolymphatic duct in Dasyatis 

 centrums. 



Fig. 9. The two endolymphatic ducts of Sphyrna zygczna. d.e.u., utricular duct. 

 S.U., the sac of the utricular duct, d.e.s., saccular duct, s.s., its sac. c.a. and c.p., 

 anterior and posterior ear canals, k., cartilaginous auditory capsule. 



Fig. 10. A small portion of one of the so-called spiral nerve bundles. The first 

 or innermost one of the outer hair cell territory. X 880. Methyl blue. 



