396 THE SKIN AND THE SENSE-OKGANS. 



and outwards under the utricle^ giving off the R. sacculi, which runs 

 downwards and outwards ; the R. rec. utriculi is then given off as 

 a number of fibres^ which run ujîwards and forwards; the main 

 nerve then divides to form the R. ampullae anterions and the R. am- 

 jmllae externae, which course together for a short distance and then 

 separate to reach their respective ampullae. The R. posterior nins 

 backwards and outwards, gives off the R. lagenae, and then divides 

 to form the R. 7ieglectus, running upwards, the R. basilaris running 

 downwards and backwards^ and the R. anipnllae posterioris which 

 courses backwards and outwards. 



(i) The utricle [iitriculus) (Figs. 247 and 248 u) is irregularly 

 cylindrical in form : commencing at the recessus utriculi it passes 

 forwards and outwards ; then backwards, inwards, and upwards, to 

 terminate at the simis jjostei'ior, where it is slightly contracted. At 

 about its middle it is divided into an anterior and a posterior part by 

 an incomplete, sickle-shaped partition, formed by the posterior 

 semicircular canal opening obliquely into the utricle, and so 

 causing a fold in the posterior w^all : on the anterior wall there is 

 no fold ; the aperture left in the partition is the apertura ^driciili. 



The posterior part of the utricle receives the sinus superior, which 

 is formed by the junction of the two vertical semicircular canals. 

 The anterior part of the utricle receives the hinder dilated end of 

 the external semicircular canal by an opening in its posterior wall, 

 close to the apertura utriculi. In the lower wall or floor is the 

 narrow opening leading into the saccule (catialis utriculo-saccularis) : 

 this opening is placed with its long axis parallel to the long 

 axis of the utricle, with its broader end posterior, and the narrower 

 end anterior. 



(2) The recessus utriculi (Figs. 247 and 248 rec). The anterior 

 end of the utricle Avidens and curves downwards and outwards to 

 form the recessus utriculi ; on its floor is a thin, kidney-shaped plate 

 or otoliths, resting on the macula ac. recessus utriculi {77m), which re- 

 ceives the ramulus rec. utriculi; under it the raniulus awp. anterioris 

 and the ramulus awp. externae run forwards and close together to 

 reach their respective ampullae, which are close together at the 

 antero-extemal wall of the recessus utriculi. The otolith is a glassy, 

 homogeneovis plate, with numerous vacuole-like spaces and striated 

 borders ; it covers the whole of the macula. 



(3) The anterior ampulla and semicircular canal (Figs. 247, 

 248, aa, ca). The anterior ampulla is a rounded, oval vesicle, 

 with a depressed roof (Fig. 250 I) ; on the floor is a transverse 



