398 THE SKIN AND THE SENSE-ORGANS. 



somewhat raised ; and in the middle it presents a small elevation 

 (Fig-. 249 cv). On the crisfa acustica rests the cupula terminalis 

 (Fig. 250 I, en] ; this is arched above but of the same form as the 

 crisfa acustica below, from which it is separated by an even slit-like 

 space ; the ends are not rounded but hollowed out. The substance 

 of the cupula is very soft and has parallel striations, formed of fine 

 fibres and running from above downwards ; it separates very easily 

 from the crisfa acustica. The anterior ampulla is directed forwards, 

 outwards, and slightly upwards, to open into the anterior semicir- 

 cular canal (canalis m. anterior) (ca), which curves first upwards and 

 forwards, then backwards, inwards, and upwards, to open by means 

 of a slightly dilated end into the sinus superior utriculi. 



(4) The external ampulla and semicircular canal (Figs. 247, 

 248 ae, ce). The external ampulla lies immediately external to the 

 anterior ampulla ; it also is an oval vesicle, and corresponds with the 

 anterior ampulla in size and shape, except that the roof is higher. 

 The roof is directed backwards, the floor forwards ; the septum 

 fransversum is low, placed vertically, and bears a triangular, slightly 

 depressed crista acustica : the broader, rounded end of the crista is 

 directed upwards, the apex downwards. The corresponding ^cupula 

 terminalis is relatively high, and is of the same shape as the crista, 

 and is striated. The external ampulla is continuous with the ex- 

 ternal semicircular canal (canalis m. externus) (ce), which courses 

 outwards and backwards ; then backwards, inwards, and slightly 

 upwards, touches the roof of the posterior ampulla; then curves 

 forwards and inwards to terminate by a slightly dilated end in the 

 anterior part of the utriculus. 



(5) The posterior ampulla and semicircular canal (Figs. 247, 

 248, and 249 ap, cp). The posterior ampulla commences at the 

 posterior end of the sinus post, utriculi, and is directed outwards 

 and backwards. It corresponds in all other points with the anterior 

 ampulla. The posterior semicircular canal (ce) (canalis m. post.}, 

 into which the ampulla opens, curves upwards, inwards, and for- 

 wards, to open into the upper end of the sinus superior. 



(6) The saccule (s), ductus endolymphaticus (fie), and the 

 saccus endolymphaticus (Figs. 247, 248, 249). The saccule (s) 

 is an oval vesicle, placed under the anterior part of the utricle and 

 directed outwards and downwards ; below it is flattened in a di- 

 rection from in front and within, outwards and backwards ; above 

 it is wider. In the inner and anterior surface is the rounded, oval 

 macula acustica sacculi (Figs. 247 and 248 ms), to which is distri- 



