Odontogenic tumors of salmon.

Teeth are present in nearly all vertebrate ani mals except turtles and birds, but tumors of these structures are seldom reported (7). Recently, we had the opportunity to examine the head of a large adult chinook salmon, Oncorhynchus Wzawytscha, and a photograph and histological see tions of a second one. Both fish were taken from displayed innumerable tumors on all tooth-bear ing surfaces. The lips of the fish are greatly deformed by lobular confluent masses that extend onto the dental surfaces of the jaws ; teeth can no longer be identified (Figs. 1 and @2). A roentgenogram of the head of the fish available for study shows no cvi dence of bone destruction. In the Salmonidae (troutandsalmon) teetharepresent notonlyon the maxilla and mandible, but also on many bones bounding the mouth ; viz., vomer, glossohyal, basibranchials, and branchial arches. Isolated tumors, usually spherical in shape, are present on these accessory dental surfaces (Fig. 3). On close inspection, small tumors may also be seen arising from single gillrakers on the branchial arches (Fig. 4). In some instances a portion of the normal gill raker can still be recognized (Fig. 5). All the tu mors are firm and rubbery in consistency, yellow white in color. On section the cut surface has a whorled fibrous pattern. MICROScOPIC APPEARANCE The teeth of most teleosts are continuously re placed during the life of the fish. The develop ment of the enamel organ and its ameloblasts from the dental epithelium and that of the dentin producing odontoblasts from the mesenchyme of the dental pap@lla (Fig. 6) are essentially the same in these fishes as in mammals (5, 6, 11). The gill rakers of some sharks (1) and sturgeons (@) are dentin-containing homologs of teeth. Among most teleosts, such as salmon, however, the supporting tissue of the gillraker is bone, and in the absence of an enamel organ the homology with teeth is doubtful (1@). The histological appearance of the tumors is characterized by the presence of irregular masses of epithelial cells often widely separated by inter lacing bundles of connective tissue. In the neo plasms arising on the gilirakers, the periphery of the epithelial nests is usually bordered by a single layer of cuboidal cells; the remaining cells are closely approximated, resembling stratified epi thelium (Fig. 7). In tumors of the tooth-bearing regions the epi thelium appears as a stellate reticulum surrounded by a layer of …