344 AVERS. 



EXPLANATION OF PLATE IV. 



Fig. I. Surface view of the apical turn of the cochlear spiral of the common 

 Mouse, to illustrate the twisted condition of the cochlear organ. X 30. a.c.c, apex 

 of cochlear organ, its distal end. cm., the cochlear herve. c.c, cochlear canal. 

 b.m., basilar membrane, h.b., hair band, l.s.o., lamina spiralis ossea. st.v., stria 

 vascularis. At c.n. and n. the variation in the amount of spiral twist which the ter- 

 minal bundles of the cochlear nerve suffer is well shown. The canal is not curved 

 equally in all its parts. The figure shows three different degrees of curvature. 



Fig. 2. Transverse section of the cochlear canal and contained structures of a 

 new-born Rabbit. X 85. Lg.s., ligamentum spirale. Set., scala tympani. sc.v., 

 scala vestibuli. The epithelial ridges are colored red; the hair band, brown. In the 

 canal is seen the remains of hair structures from source unknown. 



Fig. 3. Transverse section of the organ of Corti of new-born Rabbit, to show the 

 relations of the cellular constituents of this stage of development. X 865. There 

 are shown five rows of well-developed hair cells, and four rows of supporting cells, 

 which at this stage are also hair-bearing. The hair cells of the Sauropsid organ are 

 very numerous, c.p.c, embryonic Corti's pillar cells. 



Fig. 4. Four figures of transverse sections through the auditory region of the 

 head and through the auditory capsule of early embryos of Petromyzon Jiuviatilis. 

 After Kuppfer. 



a. Through the ingrowing ear cup and facial ganglion. The double lip of the 



upper wall of the cup is well marked. 



b. A later stage of the auditory involution, viewed in transsection through the 



middle of its longitudinal diameter. The opening through the ectoderm is 

 still persistent — endolymphatic duct. The "dorsal root" is seen to enter 

 the gap in the top of the capsule. 



c. Transverse section, to show the manner of nerve ending of the " dorsal root." 



d. The same, more highly magnified. 



Fig. 5. Three figures of transverse sections of Lacerta viridis embryos, through 

 the internal ear in three stages of its development. After Hoffmann. The mem- 

 branous ear is colored red; the nerve, black. 



a. X 36. Through an early stage of canal formation and ampulla building. The 



cochlear nerve and ganglion are in contact with the outgrowing cochlear tube. 



b. A late stage of the developing ear, to show the manner of branching of the 



nerve and its distribution to the parts of the ear. r.d.e., ramulus' sup- 

 plying the ductus endolymphaticus. 



c. A still later stage of the same. 



Fig. 6. Camera sketch of the apex of the arch of Corti of the Dog, to show the 

 relative sizes of the outer (upper in figure) and lower pillar heads. X 630. 



Fig. 7. The hair band of a young Virginia Opossum in transsection, to show the 

 shape, breadth, and thickness, and also one condition of the appendix (Randwulst 

 or Korper) to the outer edge. X 630. 



Fig. 8. Horizontal section of the cochlear organ of Petromyzon niarinus, below 

 its bifurcation. X 45. 



