Page:An Introduction to the Study of Fishes.djvu/120

92 to the trunk, accompanying the lateral line. In many fishes those of the infraorbital ring are much dilated, protecting the entire space between the orbit and the rim of the præoperculum; in others, especially those which have the angle of the præoperculum armed with a powerful spine, the infraorbital ring emits a process towards the spine, which thus serves as a stay or support of this weapon (Scorpænidæ, Cottidæ).

The pectoral arch of the Teleosteous fishes exhibits but a remnant of a primordial cartilage, which is replaced by two ossifications, the coracoid (51) and scapula (52); they offer posteriorly attachment to two series of short rods, of which the proximal are nearly always ossified, whilst the distal frequently remain small cartilaginous nodules hidden in the base of the pectoral rays. The bones, by which this portion is connected with the skull, are membrane-bones, viz. the clavicle (49), with the postclavicle (49 + 50), the supraclavicle (47), and post-temporal (46). The order of their arrangement in the Perch has been described above (p. 59). However, many Teleosteous fish lack pectoral fins, and in them the pectoral arch is frequently more or less reduced or rudimentary, as in many species of Murænidæ In others the membrane-bones are exceedingly strong, contributing to the outer protective armour of the fish, and then the clavicles are generally suturally connected in the median line. The postclavicula and the supraclavicula may be absent. Only exceptionally the shoulder-girdle is not suspended from the skull, but from the anterior portion of the spinous column (Symbranchidæ, Murænidæ, Notacanthidæ). The number of basal elements of each of the two series never exceeds five, but may be less; and the distal series is absent in Siluroids.

The pubic bones of the Teleosteous fishes undergo many modifications of form in the various families, but they are essentially of the same simple type as in the Perch.