Annual report of the Board of Regents of the Smithsonian Institution . lateral wall of thesegment, or on the basalar sclerite, as wehave seen, is intimately at-tached to the humeral angleof the wing base by athickening (a) of the inter-vening membrane. Thesubalar muscle (fig. 19, M)is always a large muscle,and, through the attach-ment (6) of the subalar scle-rite with the second axillarysclerite of the wing base{2Ax) it pulls downward onthe base of the wing imme-diately behind the fulcra!support {WP). In the dragon flies thehomologues of the basalarand subalar muscles ofother insec
Annual report of the Board of Regents of the Smithsonian Institution . lateral wall of thesegment, or on the basalar sclerite, as wehave seen, is intimately at-tached to the humeral angleof the wing base by athickening (a) of the inter-vening membrane. Thesubalar muscle (fig. 19, M)is always a large muscle,and, through the attach-ment (6) of the subalar scle-rite with the second axillarysclerite of the wing base{2Ax) it pulls downward onthe base of the wing imme-diately behind the fulcra!support {WP). In the dragon flies thehomologues of the basalarand subalar muscles ofother insects are insertedby strong tendonsthat are attached directlyon the wing bases, the first on the humeral plate (fig. 11 A, HP)the second on the axillary plate {AxP). Furthermore, the ven-tral ends of these muscles in the dragon flies take their origin on thelower edge of the pleural wall of the segment, their bases evidentlyhaving been transferred from the coxa to the body wall. In the flies(Diptera) the base of the subalar muscle has undergone a pir: Figure 19.—The pleural wing muscles of the mesothoraxof a grasshopper (Dmosieira), inner view of right , Membranous connectioii of basalar sclerites (Ba) withhumeral angle of wing base; SAx, dorsal plate of secondaxillary; SAx, third axillary; b, connection of subaiare (Sa)with second axillary; Ba, basalar sclerites; c, ventral plate axillary; Cx, coxa; D, flexor muscle of wing; E, pleu-ral basalar muscle; M, coxo-basalar muscle; M, co\o-sub-alar muscle; PIR, pleural rid^e; Sa, sulialare; tg, rudimentoftegula; If3, inesothoracic wing, turned upward HOW INSECTS FLY SNODGRASS 405 The fifth set of wing muscles are the wing flexors. The flexor ofeach wing is usually a small muscle, or a group of small muscles (, D), the fibers of which have their origin on the pleural wall of thesegment and are inserted directly on the third axillary sclerite of thewing base (fig. 12, 3Ax). The flexor muscl
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