298 THE SALAMANDER 



of the anterior and horizontal canals open. Posteriorly the utriculus 

 also turns ventrally into the sinus posterior^v^hicWis continued into the 

 ampulla of the posterior canal. The utriculus further communicates, 

 by means of an oval opening, with the sacculus. This opening, the 

 canalis utriculo-saccularis (can.utric-sac), is situated at the base of the 

 utriculus below the sinus superior, and from its mesial wall the pars 

 neglecta (p.neg.) (Retzius) is evaginated. 



The sacculus (sac.) is a lens-shaped sac, compressed in a ventro- 

 mesial plane. It contains otolith granules and communicates with 

 the saccus endolymphaticus by means of the endolymphatic duct (d.el.). 

 It also opens into the utriculus^ as already noted, and into the lagena 

 and pars basilaris. The lateral wall is extremely thin and separates 

 the sacculus from the main perilymphatic space — the spatium saccu- 

 lare. The ductus endolymphaticus (d.el.) arises from the dorso-mesial 

 aspect of the sacculus close to the canalis utriculo-saccularis and passes 

 directly dorsalwards, mesial to the utriculus and close to its wall, 

 and directly between the origins of the two vertical canals. At about 

 the level of the dorsal margin of the sinus superior utriculi the duct 

 passes through the foramen endolymphaticum into the cranial cavity, 

 where it expands into the saccus endolymphaticus (see 'Membranes of 

 the Brain', p. 121 et seq.). 



The lagena (lag.) (or lagena cochleae, Retzius) is a somewhat 

 pear-shaped pocket opening from the mesial aspect of the sacculus 

 near its posterior margin. It contains an otolith. 



The pars basilaris (p.bas.). Although both Hasse and Kuhn had 

 correctly described the pars basilaris in Salamandra, yet Retzius 

 (1881) denied its existence as a separate recess, and supposed it to 

 be represented by a small oval nerve-ending on the inner wall of the 

 upper end of the lagena. Harrison (1902) corrected this error in 

 favour of the older authors — a result which is here confirmed. The 

 pars basilaris is a small evagination from the dorso-mesial wall of the 

 lagena facing the opening of the latter into the sacculus. 



4. Nerve-endings. 



The ear is supplied by the eighth cranial nerve. The fibres of this 

 nerve terminate on plate-like areas of sensory cells, called maculae, 

 which occur at the following positions — at the ampullae of the semicir- 

 cular canals, here called cristae by Retzius, on the floor of the recessus 

 utriculi, the sacculus, xh^ pars neglecta, pars basilaris, and the lagena. 



The cristae acusticae ampullorum (Retzius) are bi-concave areas 

 lying on the ventral surfaces of the posterior and horizontal ampullae, 

 and on the anterior face of the anterior vertical ampulla. 



