. Bulletin of the British Museum (Natural History), Geology. REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES 269 and runs forward through the length of the frontal. Anteriorly it passes down into the nasalo-antorbital, where it joins the infraorbital canal. The main cephalic division of the sensory canal crosses the antero-dorsal corner of the supracleithrum and passes forward through the dermopterotic. At its point of entry into the dermopterotic, it gives off the supratemporal commissure, which runs through the extrascapular. The main cephalic division then turns down through the posterior
. Bulletin of the British Museum (Natural History), Geology. REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES 269 and runs forward through the length of the frontal. Anteriorly it passes down into the nasalo-antorbital, where it joins the infraorbital canal. The main cephalic division of the sensory canal crosses the antero-dorsal corner of the supracleithrum and passes forward through the dermopterotic. At its point of entry into the dermopterotic, it gives off the supratemporal commissure, which runs through the extrascapular. The main cephalic division then turns down through the posterior corner of the dermosphenotic as the infraorbital canal. The infraorbital canal passes round the anterior edge of the postorbitals, and down through the infra- orbitals, finally entering the nasalo-antorbital. In the nasalo-antorbital it branches into two, the anterior branch passing into the postrostral where it ends blindly just above the nasal orifice. The posterior branch continues on through the nasalo- antorbital to fuse with the supraorbital canal. Most of the above account of the Chy. Fig. 18. Ptycholepis bollensis Agassiz. Ceratohyal and hypohyal. From a specimen from the Lias of Holzmaden, Germany, in the Tubingen Museum. sensory canal system is based on specimen No. 8740 from Boll, in the Tubingen Museum. Palate. The palatoquadrate is very similar to that described by Stensio (1921 : 211) for Boreosomus arcticus, and by Brough (1939 : 63) for Ptycholepis barboi. The palato-quadrate is a large ossification consisting of three principal elements, a quadrato-metapterygoid, an entopterygoid and an ectopterygoid (Text-fig. 16). In general shape the whole apparatus is triangular with its posterior margin almost vertical. The antero-dorsal margin is strongly concave and the ossification tapers almost to a point anteriorly. The most posterior bone is the quadrato-metapterygoid and is a large high bone. Dorsally it articulates with the orbitotemporal region of the neurocraniu
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