399 



with some confidence that it would be found in the same position 

 in Ceratodus as well. 



A macula neglecta is, as he supposed, present at the same spot 

 as in Protopterus (figs. 1, 3, MN.), close behind the utriculo-saccu- 

 line passage (C.U.S.) upon the floor of the utricle. It is innervated 

 by a small twig (EN.) given off from the nerve that supplies the crista 

 of the posterior semicircular canal at the point where this nerve passes 

 outwards behind the utriculo-sacculine passage. 



It is noticeable also that in Colonel Shepherd's specimen the floor 

 of the posterior sinus of the utricle is dilated close behind the macula 

 neglecta to form a little conical diverticulum (D). A similar pocket 

 was present in both labyrinths but in the left its apex was attached 

 to the upper wall of the saccule by a small band or ligament (L.). In 



Fig. 3. Fig. 4. 



Fig. 3- Part of the left labyrinth of Neoceratodus forsten, with the saccule 

 and part of the mesial wail of the recessus utriculi removed to show the passages 

 between the utricle, sacculus, and recessus utriculi and the position of the macula 

 neglecta. 



Reference letters as in Fig. 1. 



Fig. 4. Diagram of the utricles and saccule of a shark (Carcharias). A.U. 

 utriculus anterior; A.C. U. RS. anterior utriculo- sacculine passage; M.N. macula 

 neglecta; M.R. macula recessu; P.U. utriculus posterior; P.U.S.C. posterior utriculo 

 sacculine passage. 



the space between this ligament and the utriculo-sacculine passage 

 lay the nerve to the crista of the posterior canal. 



This little dilatation may be of absolutely no importance but its 

 position is somewhat suggestive of the passage that connects the 

 posterior utricle with the saccule in Elasmobranchs. There is enough 

 evidence to suggest that the sinus superior utriculi of Vertebrates 

 other than Elasmobranchs represents a combination, probably by 

 coalescence, of the ascending arms of two canal systems such as the 

 anterior and posterior utricles of sharks (fig. 4) — the passage 



