MEMBEANOUS LABYEINTHS OF CEETAIX SIIAEKS. 



409 



of the utricles, which in this case still more closely resemble the 

 Teleosteau sinus superioris utriculi. The extra-cranial part of 

 the ductus endolymphaticus appears to make the usual forward 

 bend in close contact with the skull ; it then seems to pass 

 backwards for a . short distance, is then directed forward 

 again for a short distance in front of the first bend, passino- 

 again backwards, and finally ascending to its external opening. 

 The sacculus and lagena resemble those of Notidanus and 

 LcBmargus. 



Caechaeias lamia. Fam. Carchariids. 

 The very large size of the sacculus in this Shark results in 

 the ductus endolymphaticus immediately after its origin passino- 

 through the skull ; it there makes the usual bends, forwards and 

 backwards, and finally upwards to its external opening. The 

 recessus utriculi has similar communications wdth the utricle and 

 sacculus as in Notidanus and Lcemargus. The canalis utriculo- 

 saccularis posterior is remarkably dilated into a rounded chamber 

 shortly before its termination in the sacculus, and blending with 

 it is a like dilatation of the utriculus. The ramulus negleetus is, 

 as usual, given off by the nerve that supplies the ampulla of the 

 posterior canal. It is of unusually large size ; it sends a small 

 twig to the dilatation on the utricle, but by far the larger portion 

 is distributed to the macula on the dilatation of the posterior 

 utriculo-saceuline canal. 



EXPLANATION OF PLATE 40. 



The right membranons labyrinths of five genera of Sharks, viewed from the 

 mesial side ; all except fig. 3 are of natural size, fig. 3x2. 



a. AmpullfB. 

 a.d.c.c. Apertura ductus endolym- 

 phatici externa. 

 c.a. Canalis anterior. 

 c.c. Canalis esternus. 

 C.J). Canalis posterior. 

 d.e. Ductus endolymphaticus. 

 d.u.s:p. Ductus utriculo-saccularis 

 posterior. 



d.r.u. Ductus recessu utriculi. 

 I. Lagena cochlijE. 

 r.n. Ramulus negleetus. 

 r.x!,. Recessus utriculi. 



s. Sacculus. 

 s.e. Saccus endolymphaticus. 

 u.a. Utriculus anterior. 

 u.'p. Utriculus posterior. 



Fig. 1. Notidanus griseus. 



2. Lcemargus borealis. 



3. Laonna cornubica. 



4. Alopecias vulpos. 



5. Carcharias lamia. 



