No. I.] THE VERTEBRATE EAR. 2 1 



saccular walls which possess great interest from their unusual 

 relation to other organs of the body, particularly the central 

 nervous system, but whose morphological as well as physiologi- 

 cal significance is still entirely unknown. 



These structures are known as the otolith sacs of the brain 

 and spinal cord and as the chalk sacs covering the ventral 

 surfaces of the spinal ganglia in many Amphibia. The endo- 

 lymphatic sac is otherwise peculiarly modified, as in the oft- 

 mentioned Phyllodactylus, where it forms a large flattened shoul- 

 der sac lying beneath the skin, partly hidden by the muscles. 



That we have to deal in many of these cases with outgrowths 

 of the primitive auditory vesicle is evident, but we do not yet 

 know sufficient of their development, adult structure, and rela- 

 tions to other organs to hazard opinions as to their functions. 

 We are very much in need of further knowledge of these struc- 

 tures, and the subject will doubtless well repay the investigator. 



The endolymphatic duct, which in man is bifurcate at its 

 lower end, serves to unite indirectly the two primary divisions 

 of the ear. This condition is now seen to be a remnant of the 

 early relation of these two chambers, as may be deduced from 

 the account of the ears of Myxine, Petromyzon, and Dasyatis. 



A comparison of the ears of Myxine, Petromyzon, Dasyatis, 

 Torpedo, and Man clearly shows the connection of the duct 

 with the utricular and saccular chambers to be a fundamental 

 condition, and not a secondary acquirement, as has hitherto been 

 held. 



In the preceding account I have mentioned two tubes in the 

 Cyclostome ear, and described them as the endolymphatic ducts. 

 In Petromyzon {P. marinus and Planeri) the second tube, from 

 its position and connections, is equally entitled to be classed as 

 an endolymphatic duct. It has been figured and described by 

 only two authors, and in both instances inadequately. The rela- 

 tive size and the position of this second tube is shown in PI. X, 

 Fig. 2, D.e.s. I shall designate this tube the utricular duct, or 

 the Ductus eiidolymphaticus titriculi, while for the other tube I 

 propose the name Ductus eiidolymphaticus sacculi, or saccular 

 duct. The saccular duct is the larger of the two, having a greater 

 diameter, a larger end, and a somewhat greater length, while 

 the utricular duct, although nearly as long, tapers to its end, 

 which is only slightly enlarged. The utricular duct leaves the 



