. Bulletin - United States National Museum. Science. MONOGRAPH OF THE EXISTING CRINOIDS. 177 In a dorsal view of a postrarlial series of ossicles synarthries may be at once distinguished by their straight course across the arm taken in connection with the appearance of the point of contact between the two ossicles (repre- senting the ends of the longitudinal ridges on the two joint faces) exactly in the median dorsal line (fig. 668, p. 329: the two elements of each of the three pairs of ossicles represented are united by synarthry). Synarthries only occur between the two elements of the first
. Bulletin - United States National Museum. Science. MONOGRAPH OF THE EXISTING CRINOIDS. 177 In a dorsal view of a postrarlial series of ossicles synarthries may be at once distinguished by their straight course across the arm taken in connection with the appearance of the point of contact between the two ossicles (repre- senting the ends of the longitudinal ridges on the two joint faces) exactly in the median dorsal line (fig. 668, p. 329: the two elements of each of the three pairs of ossicles represented are united by synarthry). Synarthries only occur between the two elements of the first brachial pair and their more proximal redu- plications: that is to say. the two elements of each of the division series consisting of two ossicles, and the first two elements of division series consisting of four ossicles. Some or all of the synarthries in the postradial series in certain species may be replaced by syzygies (see p. 174), though the converse is not true. The term synarthry was first proposed by Minckert to cover all interbrachial articulations except syzygies. The synarthry as here understood was originally called bi- faseial articulation by Carpenter. The word synarthry is preferable to the term bifascial articulation on ac- count of its euphemism and brevity; it is also conveniently close to the word syzygy to suggest a relation- ship. It has seemed permissible, therefore, to adopt the word synar- thry from Minckert, but at the same time to redefine it so as to include within its meaning a single definite type of articulation. Cniptosi/narthf'i. In the slender-armed varieties of Comatula Solaris, C. pecfinata, and C. purpurea, where the synar- thries persist instead of giving place to syzygies. as in the broad-armed varieties of the same species, the apposed surfaces of the ossicles become almost plane; but a close examination reveals a faintly marked median ridge, on either side of which are the two large but very shallow and almost obsolete ligament fossae.
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