. Bulletin - United States National Museum. Science. 182 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. and part 1, fig. 32, p. 71) the course of the transverse ridge is oblique, normally making an angle of about 45° with the dorsoventral plane of the joint face, the interarticular ligament and the muscular fossae on one side of the median line con- sequently being crowded and those on the opposite side correspondingly ex- tended, and viewed dorsally the joint face is seen to cross the arm at more or less of an angle (typically about 45°) to the longitudinal axis. In an external dorsal view of a
. Bulletin - United States National Museum. Science. 182 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. and part 1, fig. 32, p. 71) the course of the transverse ridge is oblique, normally making an angle of about 45° with the dorsoventral plane of the joint face, the interarticular ligament and the muscular fossae on one side of the median line con- sequently being crowded and those on the opposite side correspondingly ex- tended, and viewed dorsally the joint face is seen to cross the arm at more or less of an angle (typically about 45°) to the longitudinal axis. In an external dorsal view of a postradial series of ossicles a straight muscular articulation may usually be at once distinguished by its straight course across the arm and by having the two points of contact mark- ing the ends of the apposed fulcral ridges equidistant fi-om the median dorsal line. An oblique mus- cular articulation, on the other hand, runs diagonally across the arms, most com- monly at an angle of from 30° to 45°, and the two points of contact are one dorsolateral, the other ven- trolateral (part 1, fig. 30, p. 71). Two oblique muscular articulations following each other are always reversed, and this alternation is the invariable rule. If the ful- cral ridge of one oblique muscular articulation crosses the joint face from a left ventrolateral to a right dorsolateral position, the. Fio. 227.—Lateral view of specimen of Perissometea Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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