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Show 1895.] AND AMPULLARY CANALS OF CHIMERA. 879 1876, mentions both the canals and cranial nerves in his paper on the skull of the Holocephali. Solger (15) in 1881 published an account of the development and minute structure of the canals; and later Garman (9) described and figured their distribution in both Chimcera and Callorhynchus. It was originally m y intention to describe at some length the cranial nerves, but lack of better material has prevented me. In the ordinary spirit-preserved material the nerves are not in a fit condition for histological work, and it is only with difficulty that the distribution of the smaller nerves can be traced. The material was purchased from the Zoological Station at Naples out of funds granted by the Council of the Eoyal Society, and I take this opportunity of expressing m y thanks and acknowledging the assistance they have given me. M y thanks are due to Professor T. W . Bridge, M.A., for his very kind assistance throughout the work, and to Mr. Gr. A. Boulenger, P.R.S., for his kindness in permitting m e to examine the series of young Chimcera and Callorhynchus in the British Museum collections. II. THE SENSORY CANAL-SYSTEM. 1. General Description. In describing the canals and branches I have not adopted the nomenclature of Garman (9), as they may be grouped into a similar series as in other fishes, and further, such a nomenclature lends itself better for purposes of comparison. I have given below, on the left side the nomenclature used in this paper, and on the right that used by Grarman. Lateral Canal = Lateral Canal. Main Canal of the H e a d = T h e Cranial Canal (part). The Occipital Commissure=Aural and Occipital Canals. The Supra-orbital Branch = The Rostral Canal. The Sub-orbital Branch = The Orbital and Sub-orbital Canals. The Maxillo-mandibular Branch=The Angular, Nasal, and Oral Canals. The lateral canal commences at the end of the long whip-like tail on the lower edge of the muscles, and passes forwards as an open groove to the region of the head, where it is continued as the main canal of the head. This passes forwards forming the supraorbital branch and in the anterior region joins with the sub-orbital and maxillary branches. Dorsally an occipital commissure is given off from the main canal, and ventrally the sub-orbital branch. Prom the angle of the sub-orbital branch a short branch is given off possibly homologous with the operculo-mandibular branch of Ganoids and Teleosts and the hyomandibular branch of Elasmo-branchs- which divides into maxillary and mandibular branches; previous to this division there is a short backwardly directed branch, tbe "jugular canal" of Garman. The maxillo-mandibular |