A treatise on zoology . e tuberculumacusticum of the medulla and associated centres. That a cranial nerve, the vagus, should supply a series of sense-organs Ieaching to the tip of the tail strongly sug•ment of the lateral-line organs in Petroiinjzon. The nervus lateralisvagi arises from a longitudinal thickening of the epiblast above the•dorsal ganglia, which is continued on the head as a series ofdorso-lateral placodes contributing to the formation of tlie gangliaof the 9th, 7th, 5th, and profundus. Similar placodes occur in thelower Gnathostomes. On the other hand, the independence of the LA
A treatise on zoology . e tuberculumacusticum of the medulla and associated centres. That a cranial nerve, the vagus, should supply a series of sense-organs Ieaching to the tip of the tail strongly sug•ment of the lateral-line organs in Petroiinjzon. The nervus lateralisvagi arises from a longitudinal thickening of the epiblast above the•dorsal ganglia, which is continued on the head as a series ofdorso-lateral placodes contributing to the formation of tlie gangliaof the 9th, 7th, 5th, and profundus. Similar placodes occur in thelower Gnathostomes. On the other hand, the independence of the LATERAL Lh\E. 4NERVE COMPONENTS 21 r;imus lateralis vagi (in the adult) from the spinal nerves, and the factthat in fish (Beard, Coilson) and in Amphibia (Harrison) thelateral-line laulimeiit grows from the head backwards in a mostindependent manner, have led most observers to believe that theorgans have phylogenetically l)een derived from the head. It isa point still unsettled. The chief functions of the organs of thelateral-line system are probably equilibration and oiientation. The sensory free nerve-endings scattered over the skin aresupplied by fibres belonging to the general cutaneous sensmysystem, and entering the central nervous system by the Oth, 7th,9th, and 10th cranial nerves, and by the succeeding dorsal roots ofthe spinal nerves. The fibres are related to the dorsal tracts of thespinal cord, and their prolongations in the medulla, including thetuberculum acusticum. It is conjectured that the acustico-lateralsystem is a specialised portion of this general cutaneous system. The nerve-fi
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
