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Show 1895.] AND A M P U L L A R Y CANALS O P C H I M E R A . 887 gradually becomes wider as it leaves the surface and finally expands into an ill-defined ampulla (PL LIII.fig. 9, a); (2) a series of tubes much smaller than number 1, all of which lead into a common tube, considerably wider, from which numerous ampullae are given off (PL LIII. fig. 9,6) ; and (3) a simple unbranched tube, at the base of which are a series of well-defined ampullae (PL LIII. fig.9,c). It is possible that ampullary canals like numbers 1 and 2 may yet be found in the Elasmobranchii: a careful investigation of the system in the Batoidei is much to be desired. The minute structure is almost identical with that of the Elasmobranchii, the chief difference being, that in the sensory organ at the base of the ampulla, in Chimcera, the epithelium-cells of the " Centralplatte" form a concavity, in which rests the " cupula terminalis" of Solger (PL LIII. fig. 10) ; whereas in the Elasmobranchii these cells are arranged as a flat plate as shown in fig. 11. Solger was the first to describe this difference. "•Bv 3. Innervation. The ampullary canals are all innervated by branches of the trigeminal1, the branches which innervate the sensory organs of the sensory canal-system giving off branches to the ampullae, as shown below :- Median group. f Supplied by dorsal branches of the ramus Posterior and anterior Supra-1 ophthalmicus superficialis (V.). orbital group. \ Posterior and anterior Sub- j Supplied by the ramus buccalis and maxillaris orbital group. 1 superior (V.). ' The ramus maxillaris inferior supplies these. Where there are a few scattered ampullary canals in the mandibular region, branches of the ramus mandibularis (V.) innervate them. Posterior and anterior Maxillo mandibular group. IV. S U M M A R Y A N D CONCLUSION. 1. In Chimcera the canals and branches persist as open grooves, agreeing in this feature with the condition which obtains in the Elasmobranchii; variations, however, sometimes occur. 2. Unlike the condition found in many Elasmobranchii, in Chimcera there are no fine dendritic branches from either the lateral or main canal, or from any of the branches of the latter. 3. Ampullary canals are present, three distinct types being found in different regions of the head. Their number, position, and even structure is subject to much variation. They are all innervated by branches of the trigeminal nerve. 4. The innervation of the sensory canals &c. proceeds from i " It is worthy of note that all the groups of ampullae-superficial ophthalmic, inner and outer buccal, hyoid and mandibular-are supplied by dorsal branches of the facial" (Ewart, 6- P- 81). |