Page:An Introduction to the Study of Fishes.djvu/111

Rh and interhæmals simple. Only the abdominal vertebræ have parapophyses, with which the ribs are articulated.

The configuration of the skull, and the development and arrangement of its component parts, approaches so much the Teleosteous type that, perhaps, there are greater differences in skulls of truly Teleosteous fishes than between the skulls of Amia and many Physostomi. Externally the cranium is entirely ossified; and the remains of the cartilaginous primordial cranium (which, however, has no vacuity in its roof) can only be seen in a section, and are of much less extent than in many Physostomous fishes. The immovable intermaxillary, the double vomer, the plurality of ossifications representing the articulary, the double articulary cavity of the mandible for junction with the quadrate and symplectic bones, remind us still of similar conditions in the skull of Lepidosteus, but the mobility and formation of the maxillary, the arrangement of the gill-covers, the development of the opercles, the suspensorium, the palate, the insertion of a number of branchiostegals on the long middle hyoid piece, the composition of the branchial framework (with upper and lower pharyngeals), are as in the Teleosteous type. A gular plate replaces the urohyal.

The scapular arch is composed entirely of the membrane-bones found in the Teleostei, and the two sides are loosely united by ligament. The base to which the limb is attached is cartilaginous; short semi-ossified rods are arranged along its hinder margin and bear the pectoral rays.

The skeleton of the hind-limb agrees entirely with that of Lepidosteus.


 * [T. W. Bridge, The Cranial Osteology of Amia calva; in Journ. Anat. and Physiol, vol. xi.]

In the Teleosteous fishes the spinous column consists of completely ossified amphicœlous vertebræ; its termination is homocercal—that is, the caudal fin appears to be more or