chap. XLI.] THE INTERNAL EAK. 327 



an acute angle from the upper outer angle of the scala 

 media to the lamina spiralis ossea. But there it is not 

 fixed on the osseous substance, but on a peculiar pro- 

 jection on this latter the arista spiralis (Fig. 163, m), 

 which is a sort of tissue intermediate between fibrous 

 and osseous tissue, and added to the vestibular surface 

 of the lamina spiralis ossea. This crista spiralis has 

 on its inner surface i.e., that directed towards the 

 scala media a deep sulcus, called the sulcus spiralis, or 

 sulcus spiralis interims ; so that of the crista spiralis 

 there are two labia to be distinguished the labium 

 vestibulare and the labium tympanicum; the former 

 being the upper, the latter the lower, boundaiy of the 

 sulcus spiralis. 



471. (3) Between the labium tympanicum of the 

 crista spiralis and the above-mentioned projection 

 of the ligamentum spirale extends, in a straight 

 direction, the membrana basilaris, forming the lower 

 wall of the scala media. The scala media is lined on 

 its whole internal surface with epithelium, this only 

 being derived from the epithelium forming the wall of 

 the auditory vesicle of the embryo, peculiarly modified 

 in certain places. The scala tympani and scala vesti- 

 buli are likewise lined with a continuous layer of 

 flattened cells an endothelium, which only on the 

 lower (tympanic) surface of the membrana basilaris 

 is somewhat modified, being composed of granular 

 looking irregular cells. 



472. As regards the scala media, the epithelium 

 lining its internal surface is of the folllowing aspect : 

 Starting with the lower outer angle i.e., where the 

 membrana basilaris is fixed to the ligamentum 

 pirale we find it a single layer of polyhedral or 

 short columnar transparent cells, lining this outer 

 angle the cells of Claudius j ascending on the liga- 

 mentum spirale, the cells become shorter, more squa- 

 mous ; such are found over a slight projection on 



