. Smithsonian miscellaneous collections. bases, and they arethus free to respond to the downward pull of the tergo-sternal close union of the terga (fig. 25) and the great size of the dorsalmuscles (fig. 34) give efificiency to the latter as elevators of the the wings are spread they are pivoted on the pleural wing proc-esses by the second axillary sclerites of their bases, and, beingclosely hinged to the terga by the first and fourth axillaries, they aresharply thrown upward when the tergal plates are depressed, andare turned downward when the terga are elevated. 96 SMI
. Smithsonian miscellaneous collections. bases, and they arethus free to respond to the downward pull of the tergo-sternal close union of the terga (fig. 25) and the great size of the dorsalmuscles (fig. 34) give efificiency to the latter as elevators of the the wings are spread they are pivoted on the pleural wing proc-esses by the second axillary sclerites of their bases, and, beingclosely hinged to the terga by the first and fourth axillaries, they aresharply thrown upward when the tergal plates are depressed, andare turned downward when the terga are elevated. 96 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 52 The mechanism for extending and flexing the wing is highly com-plex. The muscles that produce the movements of extension andflexion depend for their eiifect on the details of shape and inter-rela-tionships in the axillary sclerites, on the articulation of the scleriteswith the tergum and pleuron, on their connections with the bases ofthe wing veins, and on the structure of the wings Fig. 49- PR -The pleural elements of the wing mechanism in the mesothoraxof Dissosteira. a, thickening of cuticular membrane uniting basalar sclerites with humeralangle of wing (see fig. 48) ; sAx, second axillary; sAx, third axillary (first andfourth axillaries removed) ; b, thickening of cuticular membrane uniting subalarsclerite (Sa) with ventral plate (c) of second axillary; Ba, first basalare; c,ventral plate of second axillary resting on pleural wing process (see fig. 48) ;D, flexor muscle of wing, inserted on third axillary; E, pleuro-sternal muscle,or first pronator-extensor of the wing, inserted on basalar sclerite; M, episternalpleuro-coxal muscle, or second pronator-extensor of the wing, inserted onbasalar sclerite; M, epimeral pleuro-coxal muscle, or depressor-extensor of thewing, inserted on subalar sclerite; PIR, pleural ridge; Sa, subalare; tg, tegularrudiment; [^2, base of tegmen, showing dorsal surface. During extension and fle
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Keywords: ., bookauthorsm, bookcentury1800, bookdecade1860, booksubjectscience
