. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 490 Bashford Dean Memorial Volume. Text-figure 125. Innervation of the senson,' canal system and certain of the pit organs in Squalus acanthias. , buccalis nerve; cc, supratemporal canal; , ramus dorsalis of tenth nerve; hmc., hyomandibular canal; ioc., infraorbital canal; 1!., lateral Kne canal; IIX, lateral line nerve; mc., mandibular canal; , external mandibular nerve; os. VII, ophthalmicus superficialis of seventh nerve; po., pit organs; soc., supraorbital canal; , supratemporaHs of ninth nerve; st.
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 490 Bashford Dean Memorial Volume. Text-figure 125. Innervation of the senson,' canal system and certain of the pit organs in Squalus acanthias. , buccalis nerve; cc, supratemporal canal; , ramus dorsalis of tenth nerve; hmc., hyomandibular canal; ioc., infraorbital canal; 1!., lateral Kne canal; IIX, lateral line nerve; mc., mandibular canal; , external mandibular nerve; os. VII, ophthalmicus superficialis of seventh nerve; po., pit organs; soc., supraorbital canal; , supratemporaHs of ninth nerve; , supratemporalis of tenth nerve. From Daniel, 1934, Fig. 245; after Nonis and Hughes, 1920, Fig. 50. Hawkes, the oral, gular and spiracular are labeled HLA, HLB and HLC respectively. The preceding statements concerning the open condition of the canals hold for my four large specimens, save that on the right side of No. I the groove is lacking for a distance of about 30 mm. from the tip of the tail. A more extensive occurrence of sensory canals as open grooves is found in the Holocephali, where most of the canals, including those of the head, are open; but in the Selachii, Chlamydoselachus appears to be unique in the extent to which its sensory canals are open. The nearest approach to its condition in this respect is found in the notidanids (Daniel, 1934j, where the lateral line is an open groove as far forvv^rd as the pectoral fin. In Heptanchus the canals of the head are all closed tubes, as far back as the fifth gill-cleft. Posterior to this, the lateral lines are represented by a pair of open grooves extending almost to the tip ot the tail. In Squalus (Text-figure 125) the canals are closed excepting in the region ;ard the tip of the tail. In higher elasmobranchs, the canals are usually closed throughout their entire length. The open condition of the sensory canals found by Garman in Chlamydoselachus (Text-figure 126) is probably primitive, and in the light of all
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