In the Syngnathid, Ostracions, and other Fishes, where the exoskeleton is inordinately developed, so as to.form a suit of bony armour in which the exterior of the body is completely .covered, the endoskeleton is proportionately weak and imperfectly formed, many of the bones remaining. in a rudimentary condition. This is well seen in the osteology of the Fly ing Hippocamp, ( Pegasus draco, _fig. 4944 vvhere the bones both of the head and trunk I seem to perform quite a secondary part as contrasted with the dense tegumentary frame work covering the body. The whole face seems to be composed of a kind of snout (a), derived from the external armour of the head, in which the orbits (b) are excavated, the intermaxillary bones (d) and the lower jaw (e) alone being recognisable. The gill cvers (h) belong to the exoskeleton, while the hyoid appamtus (f) and branchial arches (g) are but very imperfectly formed. The osseous zone that sustains the pectoral fins consists of a single bone, svhich is so consolidated with the tegumentary skeleton as completely to separate the abdominal cavity from the branchial chambers ; and in the piece zn, which forms the basis of the fin itself, the usual divisions are quite undiscernible. The
vertebrx, both of the back and tail, (o, q,) are reduced to mere bony rings, While the pelvic circle, (p,) that supports the abdominal fins, (/,) is, like the rest of the skeleton, firmly con nected with the external bony armour.
In the construction of the anterior extremities a few peculiarities may be specified.
Certain genera, more especially the nide and the Cyprinidee, have attached to the dius and ulna upon their inner side a third bone, which by its anterior extremity is connected to the anterior rnargin of the os humeri, thus forming a kiud of buttress to support the fin. In the Sdaridee there likewise exist three bones in the fore-arm which at an early period come consolidated to each other, probably on account of the great strength requisite in that mce of Fishes to support the great