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Show 72 1)R. \V. G. RIDEWOOD ON THE CRANIAL [May 3, of the ectosteal articular, and developed above or around Meckel s cartilage. This gives attachment to the tendon of a part of the levator muscle of the mandible, and may be called the " sesamoid articular," thus making a third component of the articular bone. Vetter (Jena. Zeitschr. xii. 1878, pi. 13. fig. 8, /Vs.) has called attention to this bone in the Pike as a " Sesamoidverknocherung an der Insertion der Endsehne von A3-A3* an Meckel'schen Knorpel," A3 being his third or deep portion of the adductor mandibulse, and Aal its tendon. This sesamoid articular is remarkably large in Albula (text-fig. 17, p. 50), Gymnarchus, and Hyodon, in which it is set on theantero-superior side of the endosteal articular. It is of fair size in Notopterus, Osteoglossum, and Gonorhynchus; but as a rule it is small, and is situated just in front of the endosteal articular (e. g., Heterotis, Clupea), or at a short distance in advance of it (e. g., Elops, Megalops). The sesamoid articular was described in 1878 in the mandible of Belone as a " coronoid bone" by Cope (Proc. Amer. Phil. Soc. xvii. p. 695), who was of opinion that the bone occurred in no family of Teleostean fishes except the Belonidse. Gill, writing in 1895, described the bone in question as " lying mostly inside of the upper portion of the dentary " (Proc. U.S. Nat. Mus. xviii. 1895, p. 173), and, admitting that it was not in any way homologous with the coronoid of Lepidosteus, proposed to call it the " addentary" (I.e. p. 174). The relation of this bone to the dentary was, however, .based upon an error on the part of Dr. Gill. He writes (I. c. p. 173):-" This element appears to have been unnoticed by most naturalists, and to have been first observed by Dr. B. C. Briihl. In 1847 Briihl (Anfangsgriinde der vergl. Anat. aller Thierklassen, Atlas, pi. xi. fig. 17) published a figure of the disintegrated right mandible in which the supplementary bone is marked ZK. I have, however, been unable to find any reference to it in the text." As a matter of fact, only two of the four bones figured by Briihl are those of the mandible, the other two are parts of the upper jaw, and are marked ZK and OK, which abbreviations are explained on p. 88 of the text as standing for ‘ Zwischenkiefer ' and ‘ Oberkiefer' respectively. The sesamoid articular has been minutely studied by Prof. Starks, who in a letter to me dated March 15, 1904, states that it is a small ossicle situated on the inner surface of the articular, just above Meckel's cartilage, that it occurs at the lower end of the ligament (? tendon) which is attached to the articular, and that it occurs much more commonly than is generally supposed. In 1900 he published (Proc. U.S. Nat. Mus. xxii. 1900, p. 2, footnote) a list of eighteen genera of Teleostean fishes in which he had detected the presence of this " coronoid bone." Although testh occupying the position of splenial teeth, and referred to as such by Owen (Anat. of Vert. i. 1866, p. 123). occur in the mandible of Arapaima, no separate splenial is to be found in any of the fishes examined, which, being the lowest of |