CHAP, xvili.] THE SPIRAL LAMINA OF THE COCHLEA. 



77 



Fig. 137. 



Being uncertain respecting the office of this structure, we shall 

 term it the denticulate lamina (figs. 137, and 138), from a beautiful 

 series of teeth, forming its outer margin, which project free into 

 the vestibular scala, and, 

 in the first coil, terminate 

 almost on a level with 

 the margin of the osseous 

 zone, but more within 

 this margin towards the 

 apex of the cochlea. They 

 thus constitute a kind of 

 second margin to the os- 

 seous zone, on the vesti- 

 bular side of the true 

 margin, and having a 

 groove beneath them, 

 which runs along the 

 whole lamina spiralis, in 

 the vestibular scala, im- 

 mediately above the true 

 margin of the osseous 

 zone. 



tween the teeth are to be 

 seen on their upper sur- 

 face, on their free edge, 

 and also within this 

 groove, so that the teeth are wedge-shaped, and their upper 

 and under surfaces, traced from the free edge, recede. The free 

 projecting part, or teeth of the denticulate lamina form less than 

 a fourth of its entire breadth, and in the remainder of its extent it 

 appears to rest on the osseous zone; seen from above, after the 

 osseous zone has been rendered more transparent by weak hydro- 

 chloric acid, (fig. 138) rows of clear lines may be traced from the 

 teeth at the convex edge, towards the opposite or concave edge of 

 the lamina. These lines appear to be a structure resembling that 

 of the teeth themselves, and they are separated from one another by 

 rows of clear, highly refracting granules, which render the intervals 

 very distinct. These intervals, as seen in the figure, are more or 

 less sinuous and irregularly branched. 



The denticulate lamina, thus placed on the vestibular surface of 

 the osseous zone, is above, and at some distance from the plexus of the 

 cochlear nerves, which lies near its tympanic surface. The vestibular 



A. Section of the cochlear canal where the scalae are equal. 

 T"ko i-^QT.TTolc, V sv - Scala ves tit>uli. t- Scala tympani. o. Osseous zone of 

 - lamina spiralis. d. Denticulate lamina, m. Membranous zone. 

 c. Cochlearis muscle. Osseous rim of the groove of the 



ined, sv. Scala vesti- 

 tween d, denticulate 

 lamina, and m, membranous zone springing from edge of the 

 osseous zone. n. Cochlear nerves and capillaries, distributed on 



the ^P* surfa ' e of osseous zone. 



