160 ME. E. T. HiaaTNS ON THE OTOLITES OP FISH. 



skull on either side of the brain, to which. Professor Owen has 

 given the name of otocrane, and which is formed of the exocci- 

 pital, paroccipital, alisphenoid, mastoid, and postfrontal bones. 



Occasionally the lower portion of the otocranes project below 

 the true base of the skull, forming bony pouches, as may be seen 

 in the Hemiramphus and some others. 



The semicircular canals, as a general rule, are connected with 

 one another in the following order : — The anterior with the pos- 

 terior, and with the anterior termination of the external. The 

 posterior, besides its union with the anterior, is joined to the 

 posterior end of the external. At the points of union with the 

 external, each canal terminates in an ampuUa. In some cases the 

 ampullse are altogether wanting, and then each semicircular canal 

 communicates with the vestibular sac by a separate tube ; occa- 

 sionally all the semicircular canals coalesce, and join the vestibular 

 sac by one tubular prolongation. " The nerve supplying the ear- 

 chamber and its contents arises between the fifth and the vagus," 

 occasionally receiving fibres from each, and is distributed to the 

 semicircular canals, ampullse, and vestibular sac, directly over the 

 otolites, a few delicate fibrillse passing inwards to be spread over 

 the otolites. 



The acoustic purpose of this arrangement is rendered obvious 

 by an experiment performed by Camper : — 



" He filled a bag with water, and placed within it a small glo- 

 bular body which of course, from its unattached freedom, was capa- 

 ble of rolling in any direction, according to the force of an external 

 impulse." " Sustaining the apparatus in one hand, he found that 

 the slightest agitation given to the bladder was repeatedly felt by 

 the reaction of the body within." " The vibration, then, of the • 

 hard masses existing in the ears of fishes, probably augment the 

 intensity of hearing, not so much by reverberating from wall to 

 waU in the labyrinthic cavity, as by direct propagation along the 

 filaments of the auditory nerve attached to the surface of the 

 vibrating body." 



In a paper by Mr. Stoddart, " On the Organs of Hearing in 

 the various classes of Animals," published in the 'Intellectual 

 Observer,' is a statement that the three otolites are connected by 

 a ligament traversing the groove in the under surface of the largest 

 otolite. This ligament I have not succeeded in tracing, and am 

 inclined to question its existence, from the fact that the superior 

 otolite sometimes occupies a diff'erent position on the two sides 

 of the head, as may be seen in two preparations from the same 



