. The chordates. Chordata. 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
. The chordates. Chordata. 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—, 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. ; 150), these three branches running closely parallel to the respectively corresponding trig
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