9f6 MR. J. H. LLOYD AND MISS EDITS SHEtPAED OJi 



the sixth nerves, and the single foramen of the ophthalmic 

 branches of the fifth and seventh nerves (v & vii, 02).) is immediately 

 dorsal to it. 



In front of the ophthalmic foramen is a small aperture 

 which serves for the exit of the pathetic nerve (iv), and ventral 

 and slightly anterior to this is a small opening for the passage of 

 a blood-vessel (b.v.). 



The pre-auditory depression is bounded on its dorsal and ventral 

 edges by well-marked sitperior and inferior 'pre-cmdilary ridges. 

 The inferior ridge (i.p.r.) is the better developed and runs forward 

 from the auditory capsule to the olfactory capsule. The superior 

 ridge (s.jo.r.) becomes less marked anteriorly and disappears before 

 reaching the olfactory capsule. 



Membranous Labyrinth. 



As has been stated above, the posterior fontanelle of the cranium 

 contains four apertures, two on each side of the median longi- 

 tudinal line. The anterior and smaller member of each pair 

 serves to transmit the duettos endol'i/mphatictis, whilst the larger 

 posterior aperture leads into the perilymph cavity surrounding 

 the posterior vertical canal. The posterior aperture apparently 

 corresponds to the tympanic aperture described by Howes (11) in 

 Raid, and also mentioned by Goodey (6) as occurring in Ghlamy- 

 doselachus anguineus. 



Unfortunately the superficial portion of the ductus endolym- 

 phaticus was destroyed during the preparation of the skull, and 

 we are therefore unable to give any account of its course outside the 

 cranium. Judging, however, from the shallowness of the posterior 

 fontanelle, and the fact that the skin was closely attached to the 

 cranium in this region, it most probably runs straight to the 

 dorsal surfa,ce of the head. 



The meinhranous lahyrinth (text-figs. 5 & 6) of the right side 

 of the head has been dissected out, by removing the surrounding 

 cartilage, and serves as the basis of the following description. 



In this account we have adopted the nomenclature used by 

 Stewart (15) in preference to that used by Eetzius (14). 



The ductus endolymphaticus {d.e.) runs downwards and bifur- 

 cates at its lower end ; a, main branch going to the sacculus (s.) 

 and a smaller branch opening into the recessiis titriculi (r.u.). 

 Our observations on this point do not agree with those of Ayers 

 (1), who states : — " I have not seen the bifurcate endolymphatic 

 duct, described by Hasse for the species which he studied, but the 

 two endolymphatic tubes observed by E. H. Weber I have found 

 beautifully developed in Sphyrna zygcena, and there is not the 

 slightest doubt as to their occurrence." 



We have been unable to trace Hasse's statement in his paper (8) 

 or to ascertain what species he studied. There is, however, no 

 doubt whatever that the endolymphatic duct does bifurcate at its 

 lower end. The second duct present is not an endolymphatic 



