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Show 1904.] OSTEOLOGY OP THE ELOPID.E AND ALBULI1XE. 65 In Gonoi hynchus the back of the basioccipital region of the skull is hemispherical.^ lhis convexity of the occipital articulation is not, however, peculiar to this genus, for Owen and Klein have recorded the occurrence of such a convex articular surface in Fistularia (Anat. of Vert. i. 1866, p. 107; and Jahresh. Wiirtt. 1881, p. 325), and Klein in Syngnathus, Phyllopteryx, Gastero-to/ ceus, and Ostracion (Jahresh. Wiirtt. 1885, p. 108). Temporal and Preopercular Series.-The post-temporal is a constituent of the pectoral girdle rather than of the skull, but a description of the skull can hardly be considered complete unless mention be made of the manner in which the attachment with the shoulder-girdle is effected, and this, very naturally, leads to a consideration of the post-temporal bone itself. The post-temporal bone is no doubt primarily a scale-bone of the sensory- canal series. It carries the lateral line forward to the supratemporal bone, and the forward limb of the post-temporal is fairly well developed in Engraulis and Chirocentrus. The other two limbs, to the epiotic and opisthotic respectively, are usually much larger and better defined than the forward limb that passes towards the supratemporal and squamosal. The extremity of the epiotic limb is usually loosely attached above the epiotic prominence by a broad, short ligament, but in Chatoessus the connection is much more intimate and the freedom of play is greatly restricted. In Noto-pterus the epiotic limb is wanting. The opisthotic limb of the post-temporal is absent in Alepo-cephalus, Coilia, and the Mormyridse ; in Gymnarchus both epiotic and opisthotic limbs are wanting. In Engraulis the opisthotic limb is attached to the back of the exoccipital in the absence of a distinct opisthotic bone. The opisthotic limb lies deeper than the epiotic limb, and appears not to be part of the dermal bone at all, but rather one of the numerous intermuscular bones, at the back of the cranium, which has acquired a secondary connection with the post-temporal. The limb is always more or less rod-like (except in Megalops), and unlike the two more superficial limbs. In Clupea Jinta and in Chanos it forms the outermost element of a series of three nearly parallel intermuscular bones, which gradually increase in size from within outwards. The innermost of the three is attached to that part of the exoccipital which forms the lateral boundary of the foramen magnum; the second is attached to the exoccipital bone midway between this point and that process of the opisthotic to which the deep limb of the posttemporal is attached. The posterior ends of the inner and middle rods spread out like stiff brushes among the trunk-muscles. In Chirocentrus there are three brushes of tendon-bones on each side of the back of the cranium; one arises from the exoccipital immediately dorso-laterally to the vertebral articulation, the second from the exoccipital a little more laterally, and the third from that part of the exoccipital that touches the mesial edge of the opisthotic. This last tendon-bone lies immediately mesial to P roc. Z ool. Soc.- 1904, Y o l . IT. No. V. 5 |
