448 NERVOUS SYSTEM. 



ing observations have been made by M. Brugnone, of Turin,* 

 where he had adopted the precaution of previously freezing the 

 bone, so that none of the fluid could be said to have been lost 

 by accident. From the frequency with which this deficiency 

 was observed, his opinion seems to be well founded, that it is 

 the most natural state of the labyrinth. 



The parietes of the membranous labyrinth are very thin and 

 transparent; there is a very loose cellular tissue between them 

 and the bone, and they are susceptible of being highly coloured 

 by injection. 



A fluid of the same character with the preceding also fills 

 the scalae of the cochlea, and extends itself into the bony ves- 

 tibulum and the bony semicircular canals upon the outer sur- 

 face of the membranous labvrinth. 



Of the Aqueducts of the Ear. 



The Aqueducts (Aquceductus) of Cotunnius, as they are called 

 after their discoverer, are two small canals which go through 

 the petrous bone from the labyrinth. There is one for the ves- 

 tibule, and another for the cochlea. 



The Aqueduct of the Vestibulum commences in the latter ca- 

 vity, somewhat in advance of the common orifice of the two 

 semicircular canals; it goes inwards and opens on the posterior 

 face of the petrous bone, behind the meatus internus. It en- 

 larges gradually in its course, which causes it to have somewhat 

 of a triangular shape, and it is lined by a continuation of the 

 dura mater. It is about four lines long. 



The Aqueduct of the Cochlea commences in the Scala Tym- 

 pani, near the foramen rotundum, and, enlarging in its course, 

 terminates on the under surface of the petrous bone, in the in- 

 ternal margin of the jugular fossa, at the root of the little 

 spine which separates the eighth pair of nerves from the jugu- 

 lar vein. 



The anatomistf from whom these canals were named, and 

 who first described them, was under an impression that the fluid 



* Mem. de Turin, 18051808. 



f Dominici Cotunnii, Anat. Dissert, de Aquzeduct, Naples, 1761. 



