NO. 2 HONEY BEE — SNODGRASS 35 



scoop-shaped plate, broad anteriorly, tapering and rounded posteriorly 

 (I, J, m), set approximately horizontally on the upper edges of the 

 wing plates. The space between the wings is thus converted by the 

 bridge into a short channel, which gives passage to the nerve cords, 

 and hence may be termed the neural foramen (H, J, K, n/). The 

 lateral extremities of the bridge (/) are closely articulated with the 

 posterior angles of the horizontal apodemes of the episterna (D, E). 



The prothoracic endosternum of the bee does not have the structure 

 of an ordinary Y-shaped sternal "furca," in which the divergent arms 

 are the primary sternal apophyses carried inward by a median sternal 

 inflection that forms the stalk of the fork. In the bee the posterior 

 lateral thickenings that brace the median plate (fig. ii, H, I, i) appear 

 to be independent ingrowths from the furcasternum and evidently 

 represent the usual pair of sternal apophyses, which, while retaining 

 their bases on the sternum, have united with the posterior end of the 

 median plate. The supraneural bridge may be regarded as a secondary 

 formation produced by the union of flat mesal outgrowths from the 

 divergent wing plates. 



Various aspects of the prothoracic endosternum are shown in figure 

 II. At B and E the endosternum is seen in place within the prothorax, 

 with its lateral extremities articulating against the pleura. H gives a 

 posterior view looking through the neural foramen, only the posterior 

 end of the upturned furcasternum being visible. At I the endosternum 

 and sternum are shown from the left side, the basisternum being 

 horizontal, the furcasternum steeply ascending. J gives an antero- 

 dorsal view of the same parts, showing the endosternal wings diverg- 

 ing upward from the median basal ridge and united by the supraneuraj 

 bridge. At K the sternum and endosternum are shown from below 

 as seen when the furcasternum is turned horizontally. 



The prothoracic muscles. — The musculature of the prothorax com- 

 prises (i) muscles that move the head directly, (2) dorsal and ventral 

 intersegmental muscles between the prothorax and the mesothorax, 

 (j) muscles that move the propleura, or the entire propectus, which 

 probably effect indirectly movements of the head, and {4) muscles 

 of the legs. 



The direct muscles of the head are attached on the margins of the 

 foramen magnum, not in the usual manner on a postoccipital ridge. 

 They include four pairs of levator muscles and one pair of depressor 

 muscles. Two pairs of the levators take their origins on the pre- 

 phragma of the mesothorax (fig. 12 A), one pair {40) being median, 

 parallel, and inserted on the head laterad of the apical notch of the 

 foramen magnum (B, 40), the other pair (A, 41) lateral in origin, 



