488 Bashford Dean tAemorial Volume 



The posterior is larger and is closed with soft subcutaneous tissue. It is an opening into 

 the perilymph cavity surrounding the posterior vertical canal, and seems to correspond to 

 the tympanic aperture which Howes (1883) described in Raid. Before proceeding further, 

 I may mention that in this account I am following the nomenclature used by Stewart (1906), 

 which differs somewhat from that used by Retzius (1881) in his great monograph. 



The ductus endolymphaticus, on emerging from its cranial foramen, soon expands 

 into the saccus endolymphaticus. The latter lies partly in the parietal fossa and is partly 

 attached to the under surface of the skin covering this region. It is fairly regular in shape, 

 somewhat rounded on its anterior surface, and extends posteriorly in a slightly outward 

 direction, gradually becoming attenuated until it reaches its external aperture, which is 

 quite small. Internally the ductus endolymphaticus leads into the sacculus. This is not 

 rounded, but is laterally flattened, and gives off at its postero-inferior end the lagena in the 

 form of a simple caecum. 



The utriculus in this species is like that in other Elasmobranchs, being divided into 

 two portions, anterior and posterior, which do not communicate directly with each other, 

 but indirectly through the sacculus. 



The anterior utricle is rather laterally compressed and gives off the anterior canal 

 dorsally. The latter curves forward and slightly outward, and describes almost a semicircle 

 in its course, expanding at its lower end into the anterior ampulla, which then opens by 

 a wide portion into the lower end of the utricle again. 



The recessus utriculi is a somewhat spherical structure on the inferior and outer border 

 of the anterior utricle. It communicates with the latter by means of a slit-like aperture just 

 below that leading into the ampulla externus. The anterior utricle does not open directly 

 into the sacculus, but communicates indirectly with it through the recessus utriculi, which 

 opens into the sacculus by means of a rounded aperture on the posterodorsal side of the 

 recessus. 



Arising from the dorsal end of the anterior utricle, and proceeding in a posterior and 

 outward direction, is the external canal, which bends downward and comes to lie in an 

 almost horizontal position. At its anterior end it is slightly elevated and expands into the 

 ampulla externus, which communicates with the anterior utricle again by means of a short 

 canal which rests on the upper side of the recessus utriculi, but does not open directly into it. 



The posterior utricle, which is situated more internally than the rest of the labyrinth, is 

 somewhat cylindrical in shape and is slightly curved upon itself. It communicates directly 

 with the sacculus by means of a short, almost vertical canal, the ductus utriculo-saccularis 

 posterior. Arising from its dorsal end is the posterior canal, which curves outward and 

 downward, and then expands into the posterior ampulla, which opens into the lower end of the 

 utricle again. 



All three canals, anterior and posterior vertical, and external horizontal, are not rounded 

 in section, but are markedly flattened, so that their height is equal to about twice their width. 

 The external canal in its almost horizontal position lies with its compressed sides in the 

 horizontal plane. 



Goodey then continues with an account of the nerve supply of the membranous 

 labyrinth. In conclusion, he states that in structure and. in the distribution of the nerve 

 supply the membranous labyrinth of Chlamydoselachus resembles rather closely that of 

 J^otidanus (Hexanchus) griseus figured by Stewart, 1906. The membranous labyrinth 

 of Heptanchus is described and figured by Daniel (1934). 



