OTOLITHS. 121 



petrosa by a cgecal dilatation, and divides near the sacculus 

 into two hollow ducts, of which one is continuous with the 

 sacculus rotundus, whilst the other joins the utriculus; by this 

 means the cavities of the two sacculi appear to be connected. 

 On making a transverse section of the aquseductus vestibuli 

 I have observed a moderately large convolute of vessels on one 

 portion of its wall, and must therefore support the statement 

 of Hyrtl, that it is destined for the reception of veins. 



The canalis reuniens is limited to the sacculus rotundus. 

 It was discovered by Hensen, and its existence corroborated by 

 Reichert, Henle, and myself; it is attached to the periosteum, 

 and is distinguished histologically from the wall of the saccu- 

 lus only by the greater delicacy of its structure. This little 

 canal brings the sacculus rotundus into connection with the 

 ductus cochlearis, so that this forms the blind vestibular end of 

 the most important cochlear segment of the labyrinth, just as 

 the utriculus forms the blind vestibular end of the membranous 

 labyrinth. 



5. OTOLITHS. 



The otoliths contained in the albuminous endolymph of the 

 membranous labyrinth present many variations in different 

 animals, in regard to their consistence, size, and form. They 

 adhere tolerably firmly together by means of a clear tenacious 

 substance. In Reptiles and osseous Fishes the delicately formed 

 otoliths attain a considerable size, whilst in Birds, Mammals, 

 and Man they either appear to be amorphous or are crystallized 

 in the form of small rhombs, hexahedra, or octahedra. Oto- 

 liths of various size and form may however be found in the 

 same animal. 



Three or four otoliths of exceedingly pretty form occur in the 

 osseous Fishes, where they are found both in the sacculi and in 

 the ampullae. In Man and Mammals they form the white spots 

 of the maculse acusticse, and both here and in other animals 

 they are maintained in position by a tenacious gelatinous sub- 

 stance, which Lang has described in the Cyprinoids as a 

 peculiar fenestrated membrane (but which is regarded by 

 Kolliker as a cuticular formation). 



Deiters and Hasse admit the presence of a fenestrated outi- 



