A treatise on zoology . ontanelle of the skull; butthere is no pineal eye. As in many other fish, the lobi inferiores andsaccus vasculosus are well developed in the infundibular cerebellum is very large and often convoluted ; the restiformbodies, at the sides of the medulla, may also be prominent. PAIRED FINS 127 The phosphorescence of Elasmobranchs, mentioned by Aristotle,appears to be due to special little organs scattered over the skin(Burckhardt [71], Johann [2-46]). The median fins are always subdivided; the caudal is heterocercalin internal structure, thougli the axis is almos
A treatise on zoology . ontanelle of the skull; butthere is no pineal eye. As in many other fish, the lobi inferiores andsaccus vasculosus are well developed in the infundibular cerebellum is very large and often convoluted ; the restiformbodies, at the sides of the medulla, may also be prominent. PAIRED FINS 127 The phosphorescence of Elasmobranchs, mentioned by Aristotle,appears to be due to special little organs scattered over the skin(Burckhardt [71], Johann [2-46]). The median fins are always subdivided; the caudal is heterocercalin internal structure, thougli the axis is almost straight in manyliving sharks. The endoskeleton of the paired fins is very variable in detail,owing to concentration and fusion of the Iadials (somactidia). Alarge number of segments contribute to their formation—generallyten or more. The pectoral fins have a well-marked outstandingmuscular lol)e, supported by a rhipidostichous skeleton (p. 106). Gegenbaur, in 1865, attempted to show, in an important work \ V. Longitudinal section of the brain of Acanthias. (After Jolinston.) ccr, cerebellum; eji,epiphysis; h, nucleus habeuulae; , lobus inferior; , lobus lineae lateralis; , lobusvisceralis ; m, medulla ; , optic cliiasnia ; par, paraphysis ; r, roof of fourth ventricle; ,recessus neuroporicus ; , reeessus praeopticus ; sp, spinal cord ; , saccus vasculosus ; ,tuberculum acusticum ; td, telencephalon ; , tectum mesencephali; v, velum transversum. [153], that the ground-plan of the pectoral-fin skeleton consisted ofthree basal pieces, the pro-, meso-, and metapterygium, articulatedto the girdle, and each bearing a number of raclials. Later, hecompared this skeleton to the archipterygium of Ceratodiis [157].The pro- and mesopterygiura were considered to he formed bythe fusion of the basal joints of the preaxial radials. The meta-pterygium, on the contrary, with sometimes some distal elements,was supposed to represent the original axis. Vest
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