776 SPECIAL HISTOLOGY. 



constitute a peculiar vascular tract in the scala vestiluli, immediately 

 under the lig amentum spirale, the stria vascularis of Corti, and which 

 though continuous with the vessels of the periosteum, still lies above it, 

 imbedded, as it were, in the partially colored epithelium. In the zona 

 spiralis, we find in the osseous portion, but also in the nervous expan- 

 sion itself, a rich capillary plexus, continuous with a vas spirale running 

 on the under or vestibular surface of the zona meml>ranacea, through 

 the whole extent of the cochlea. This vessel, which is probably venous, 

 lies immediately under the halenula denticulata, sometimes 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 of 

 a line in diameter ; but towards the base, it gradually enlarges to 

 0-013 of a line, and is distinctly composed of two coats. In rare 

 instances, there are two capillary vasa spirala in the situation above 

 indicated, and on two occasions, in Man and in the Sheep, Corti 

 also noticed an external vas spirale, near the lig amentum 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 0-002-0-005 of a line, are very readily de- 

 stroyed, and have only a delicate neurilemma. Among these, in the 

 trunk itself and in the vestibular and cochlear nerves, there occur nu- 

 merous bipolar, apolar, and unipolar, pale and colored ganglion-cells, 

 measuring, in the Mammalia and in Man, 0-02-0-07 of a line, 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 Czerm&k in the 

 ultimate ramifications in the ampullce 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 Reiss- 

 ner 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 inversion, in which the cellular layers corresponding to the epider- 

 mis, principally, but not alone, as Remak believes, take part, the audi- 

 tory nerves are afterwards continued from the brain ; and from the 

 middle germinal layer are afforded the hard tissues and the rest of the 

 soft parts in order to complete the sentient organ. With respect to the 



