Integrative Systems 



165 



Fig. 150. Head of pollack, showing lateral-line canals and nerves of the lateralis 

 system. Lateralis nerves are black, canals and brain dotted, (o) Buccal ramus of 

 VII nerve; (dl) dorsal ramus of lateralis of X nerve; (h) hyomandibular nerve; 

 {hm) hyomandibular line of organs; (jo) infraorbital line; (/) lateral-line canal; 

 (n) nares; (o) olfactory lobe; (op) operculum; (os) superficial ophthalmic nerve; 

 (so) supraorbital line of organs; (soc) commissure connecting lines of the two sides; 

 (si) supratemporal part of lateral line; (vl) ventral ramus of lateralis of X nerve; 

 (X) visceral part of X nerve. (After Cole. Courtesy, Kingsley: "Comparative 

 Anatomy of Vertebrates," Philadelphia, The Blakiston Company.) 



canals is the lateral-line canal, which extends from head to tail along 

 the side of the body at the level of the horizontal septum separating the 

 epaxial and hypaxial parts of the body-muscle. In the region of the 

 head, the canals are arranged in a more or less complex branching sys- 

 tem (Fig. 150). In some fishes, the neuromasts lie in open superficial 

 grooves instead of deep canals. In round-mouthed eels and amphibians, 

 each neuromast is in a separate pit. They are not always arranged in 

 rows, but may be scattered over localized areas of skin — e.g., on the 

 heads of sharks are patches of pores, each pore leading into a deep pit 

 at whose bottom are neuromasts. These scattered structures are known 

 as organs (or ampullae) of Lorenzini. 



The neuromasts are probably stimulated by low-frequency vibra- 

 tions in the water, or possibly by currents in the water or by pressure. 



A special division of the facial nerve, having its separate ganglion, 

 supplies most of the lateral-line organs in the region of the head. Of this 

 division, there are three main branches, the ophthalmic, buccal, and 

 external mandibular (Figs. 147 .6; 150), these three branches running 

 closely parallel to the respectively corresponding trigeminal trunks, 

 the ophthalmic, maxillary, and mandibular. In each locality served by 

 this double innervation, the facial fibers go exclusively to lateral- 



