4 o 



MORPHOLOGICAL TYPES 



The utricle bears three semicircular canals, at the base of each 

 of which is a swelling or ampulla containing an organ of 

 balance. The whole ear is to be regarded as a very much 

 enlarged lateral-line organ. 



Eye. — The eyes are hollow cups with sensitive retinal 

 layer, iris, pigment layer, vascular choroid, and protective 

 cartilaginous sclerotic. Fitting into the aperture of the eye- 



- - -de. 



FlO, 21. — Scyllium : view of the outer side of the left auditory sac. 



a, ampulla ; 06, 2c, and /v. anterior, lateral, and posterior semicircular 



canals ; Jc. ductus endolymphaticus : s, saccule ; If, utricle. 



cup is the spherical lens, which is attached to the cup by a 

 ventral ciliary muscle. 



The movements of the eyeball are effected by six muscles. 

 Four oi these (superior, internal, inferior, and external rectus 

 muscles') exert straight pulls on the four cardinal points of the 

 eyeball, and turn it upwards, forwards, downwards, or back- 

 wards respectively. The two others (superior and inferior 

 oblique muscles) pull it obliquely either forwards and upwards 

 or forwards and downwards. 



Nose. — The nose is formed by a pair of pits on each side 



