542 PISCES—-FISHES. 
ventral (motor) roots. The first sixteen or eighteen nerves 
form the brachial plexus, which supplies the pectoral fin. 
The sympathetic system consists of a longitudinal gang- 
lionated cord along each side of the vertebral column. 
of ch ch Ino 
Fic. 284.—Side view of chief cranial nerves of Elasmobranchs, 
—-Slightly modified from Cossar Ewart. 
olf., Over olfactory nerve; ch., over cerebral hemispheres ; cd., over 
cerebellum ; 7z.0., over medulla oblongata; 7., mouth; mx., 
maxillary branch of 5; 2.5, mandibular branch of 5 3 2.7, 
mandibular branch of seventh nerve ; @.1~5, groups of ampulla ; 
0.8.5, superficial ophthalmic of § ; 0.f., ophthalmicus profundus ; 
0.8.7, superficial ophthalmic of 7; JV., nostril; 3, oculomotor ; 
e.g., Ciliary ganglion; 5, trigeminal; 7.4., inner buccal; 0.d., + 
outer buccal ; 74., buccal of 7; 2., palata: of 7; sf., spiracle ; 
ch., chorda tympani; 7.47., hyomandibular of 7; 8, auditory; 
£., ear; 9, glossopharyngeal ; 10, roots of vagus ; ¢.10, lateral 
nerve of vagus ; 7.10, intestinal nerve of vagus ; 1’-s’, gill-clefts. 
Sense organs.— 
(a) The eyes (see p. 495). The iris has a fringed upper margin. 
(6) The ears (see p. 493). The vestibule is connected with the sur- 
face by a delicate canal—the aqueductus vestibuli—a remnant 
of the original invagination. A small part of the wall of the 
auditory capsule is covered only by the skin, forming a kind of 
tympanum. Within the vestibule are calcareous otolithic par- 
ticles surrounded by a jelly. 
(c) The nasal sacs are cup-like cavities with plaited walls. 
(d@) The sensory tubes are best seen on the ventral surface, where 
they lie just under the skin. At their internal ends lie ampullee, 
containing sensory cells. At their outer ends there are pores. 
It is probable that they are organs partly of touch, and partly 
of ‘‘ chemical sense.” 
Alimentary system.—The mouth is a transverse aperture ; 
the teeth borne by the jaws are numerous, and those worn 
away in front are replaced by fresh ones from behind ; naso- 
