THE EAR. 413 



venous, lies immediately under the habenula denticulata, some- 

 times more towards the interior, sometimes more externally, 

 becoming, in the last half turn of the cochlea, a capillary vessel 

 of not more than 0-004/" in diameter ; but towards the base, 

 it gradually enlarges to O013'", and is distinctly composed 

 of two coats. In rare instances, there are two capillary vasa 

 spiralia in the situation above indicated, and on two occa- 

 sions, in Man and in the Sheep, Corti also noticed an external 

 vas spirale, near the ligamentum spirale on the zona pectinata, 

 which, however, did not communicate with the internal vessels, 

 so that, speaking generally, the zona pectinata is non-vascular. 



Lastly, we have to consider the acoustic nerve. The fibres 

 of its trunk, in Man, measure 0*002 — 0005'", are very readily 

 destroyed, and have only a delicate neurilemma. Among 

 these, in the trunk itself and in the vestibular and cochlear 

 nerves, there occur numerous bipolar, apolar, and unipolar, 

 pale and coloured ganglion-cells, measuring, in the Mammalia 

 and in Man, 002 — OW", of which the two latter forms 

 are, as Stannius correctly observes, probably only truncated 

 bipolar cells, inasmuch as, particularly in Fishes, the acoustic 

 nerve contains cells of this kind only or nearly so. Similar 

 cells, but smaller, are also met with, as already mentioned, in 

 the cochlea, as well as in the nervous twigs in the vestibule 

 (Pappenheim, Corti). Divisions of the fibres of the auditory 

 nerve were noticed by Czermak in the ultimate ramifications 

 in the ampullae and sacculus of the Sturgeon, by myself and 

 Harless in the Frog, and by Leydig in the Chimcera. 



Of the development of the auditory organ, it need here 

 merely be mentioned, that according to Huschke's discovery, 

 confirmed by Eeissner and Remak, the membranous portions 

 of the labyrinth are formed from the external integument, 

 simply by its inversion, and consequently in their origin may 

 be compared with the lens and vitreous body. To this in- 

 version, in which the cellular layers corresponding to the epi- 

 dermis, principally, but not alone, as Remak believes, take part, 

 the auditory nerves are afterwards continued from the brain ; 

 and from the middle germinal layer are afforded the hard tis- 

 sues and the rest of the soft parts in order to complete the sen- 

 tient organ. With respect to the histological development of 

 the soft parts of the labyrinth, nothing of consequence is known. 



