The Anatomy of the Pectoral Fin in Sarotherodon Niloticus Trewavas* (Cichlidae)

The pectoral fin of the teleost fish Sarotherodon niloticus is described, emphasizing the joints of the rays and the insertions of the muscles onto the rays. In each ray joint, two axes of movement perpendicular to each other are present. The first ray, in combination with the second, articulates directly on the scapula. The other rays articulate on the proximal radials by means of a common fibrocartilage pad. Models are given to illustrate the principles of these joints. An account is given of the musculature of the pectoral fin. The insertions on the rays are shown in detail. The possibilities of the effects of muscle action on the rays are discussed. It is demonstrated that the abductor as well as the adductor muscles can effect multidirectional movements of the rays.