DISSECTION OF THE SHARK 31 



line fibers of the vagus arise by a large root farther forward 

 (rostral) than the other vagus roots. 



18. The acoustico-lateral complex. The membranous laby- 

 rinth and the lateral line organs comprise a complex system of 

 sense organs with many features in common (see Johnston 

 ('06), Chap. VII). Within the lateral line canals and ampullae 

 of Lorenzini are found sense organs which resemble those of the 

 internal ear, and the nerves which supply them enter the same 

 part of the brain, the area acustico-lateralis (see Section 22 and 

 Figs. 2 to 5) . The sense organs of the saccule in fishes are sen- 

 sitive to sound waves; those of the ampullae of the semicircular 

 canals assist in maintaining equilibrium; and those of the 

 lateral line organs are sensitive to water vibrations of a slower 

 rate than the sound waves received by the ears, with possibly 

 other functions in addition. 



The nerves terminating in the area acustico-lateralis consti- 

 tute a functional and anatomical system distinct from all other 

 sensory nerves, though peripherally they may be bound up in 

 the same nerve-trunks with other components. They are 

 most closely related with the general cutaneous nerves. They 

 reach their peripheral end-organs through the following nerve 

 trunks (cf . the next section) : 



(1) For the supra-orbital canal from the supra-orbital trunk 

 (this component of this trunk is called the ramus ophthalmicus 

 superficialis VII). 



(2) For the infra-orbital canal from the infra-orbital trunk 

 (this component is called the ramus buccalis VII) . 



(3) For the hyomandibular canal from the facial trunk or 

 hyomandibular nerve (called the ramus mandibularis externus 

 VII). 



(4) For the internal ear from the nervus acusticus. 



(5) For the lateral line organs of the temporal canal (ramus 

 supratemporalis IX). 



(6) For the lateral line canal of the body from the ramus 

 supratemporalis, ramus dorsalis, and ramus lateralis X. 



The nerve fibers of this system which supply the irregularly 

 arranged ampullae of the head distribute in company with those 

 for the lateral line canals of the head. 



19. Many of the peripheral nerve-trunks are mixed in the 



