190 
4.—Tuer Har (Fig. 24). 
The auditory nerve is described with the other 
cranial nerves. 
As in Teleosts generally the ear is only externally 
enclosed by the ear ossicles. Hence it projects freely into 
the skull cavity internally, and is only separated from the 
brain by its own and the brain membranes. 
The utricular sac consists of a central chamber (uér., 
often divided into three portions, two of which constitute 
the utriculus sensu stricto and the third the posterior 
utricular sinus), and a wide ventral chamber or superior 
utricular sinus or canal commissure (uér.'). These, how- 
ever, may conveniently be called the central and vertical 
chambers of the utriculus. From the anterior end of the 
central chamber connections are effected with the ampulle 
of the anterior and external semicircular canals, at the 
posterior end with the ampulla of the posterior semi- 
circular canal and the other extremity of the external 
canal. The vertical chamber rises up almost at right- 
angles from about the centre of the central chamber, and 
receives above the upper extremities of the anterior and 
posterior semicircular canals. There is only one sense 
organ in the utriculus, the macula acustica recessus 
utriculi (m. 7. w.), situated in a slight depression of the 
central chamber in front (Recessus utriculi). The three 
semicircular canals are disposed as follows :— 
Canalis anterior (a. s. c.).—Just above its connection 
with the central chamber of the utriculus it swells into a 
large ampulla anterior (amp. a.), the outer wall of which 
bears a transversely extending sense organ and ridge, the 
crista acustica ampulle anterioris (ant. cr.). Above, the 
canal passes upwards and backwards into the vertical 
utricular chamber. 
