. A manual of zoology. Zoology. 500 CHORDATA. it divides into several curved lines (fig. 5S9, SI). It is caused by a groove or a canal beneath the scales which opens to the exterior by numerous canals through the scales. The special sense organs (neuromasts) lie in the epithelium of the canals. They may also occur in'special pits in the skin {ampulhc of Loroizini, Savi's vcsidc's of the elasmobranchs), or they may occur separated in several rows (Amphibia). Those of the head are innervated by branches of the facial nerve, those of the trunk by the lateralis branch of the vagus. These nerves ha
. A manual of zoology. Zoology. 500 CHORDATA. it divides into several curved lines (fig. 5S9, SI). It is caused by a groove or a canal beneath the scales which opens to the exterior by numerous canals through the scales. The special sense organs (neuromasts) lie in the epithelium of the canals. They may also occur in'special pits in the skin {ampulhc of Loroizini, Savi's vcsidc's of the elasmobranchs), or they may occur separated in several rows (Amphibia). Those of the head are innervated by branches of the facial nerve, those of the trunk by the lateralis branch of the vagus. These nerves have their cerebral connections in close association wth the auditory nerve, which would imply a similarity of function. Since these organs are lacking in mammals and man it is difficult to determine their function. Experiment seems to show that thev are for the preception of water cu'-rents and indirectly the proximity of solid bodies. ^Mention has already been made of the nerve end buds (taste) which, besides occurring in the skin, are especially abundant in the mucous membrane of the mouth as well as on the lips and barbels The alimentary tract is spacious oitly in the orophar}-ngeaI region. Then it narrows to a slightly convoluted tube in which the ^•arious regions. Fig. 550.—Digestive tracts of (.4) Squatina vulgaris (.partly opened) and (B) Tra- cliiinis ratlialus (from Gegenbaur). ap, pyloric ca'ca; c, rectum; (/, bile duct; dp, duct of air bladder; ;, intestine; Of, oesophagus; p, pylorus; v, stomach; vs, spiral gland; -T, rectal gland. are not sharply marked off from each other. ^Touth and pliarynx fre- quently bear teeth. In the teleosts the bones of the roof of the mouth and the visceral arches may be covered with coalesced heckel-like teeth. lit the elasmobranchs the lining of the mouth, like the extental skirt, is frequently covered with small dermal scales; the large chewing teeth are conhned to the edges of the Meckelian and pterygocpiadrate arches, where they
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
