8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



latter extends upward from the mandibles almost to the bases of 

 the antennae beneath the strongly arched epistonial sulcus (es). The 

 expansion of the clypeus is directly correlated with the great number 

 of muscle fibers attached on its inner surface, which constitute the 

 dilator muscles of the internal sucking pump (fig. lo A, C). 



On the back of the head (fig. i B) the opening into the neck, the 

 foramen magnum (For), occupies a central position, and below it is 

 the deep excavation of the cranial wall known as the fossa of the 

 proboscis (PF), having a membranous floor in which are implanted 

 the bases of the maxillae (Mx) and the labium (Lb). To the inflected 

 sides of the fossa are articulated the rodlike maxillary cardines (C, 

 Cd). Between the foramen and the fossa the broad postgenal walls 

 of the cranium are connected by a subforaminal bridge. The median 

 part of the bridge clearly is of hypostomal derivation, but the 

 hypostomal element (D, HB) is constricted between a pair of 

 mesally directed postgenal lobes (PgL). In Vespidae the postgenal 

 lobes themselves are united in a postgenal bridge, and the more 

 primitive hypostomal bridge is reduced to an internal ridge connect- 

 ing an exposed subforaminal remnant with the hypostomal margin 

 of the fossa. Thus, as stated by Duncan (1939), the subforaminal 

 bridge of Vespida "consists chiefly of postgenal structures, though 

 it does include a hypostomal component." In Apis, on the other 

 hand, the bridge is chiefly hypostomal, but includes postgenal 

 intrusions. 



At the sides of the foramen magnum are the long posterior ten- 

 torial pits (fig. I B, D, pt), from which there extends forward and 

 downward in the head a pair of strong tentorial bars (C, E, AT) 

 attached anteriorly on the ridge of the epistomal sulcus (C, ER) , 

 with their roots marked externally by a pair of pits in the groove 

 (A, E, at). These bars, except for their extreme posterior ends, 

 represent the anterior arms of the tentorium as this structure is 

 developed in more generalized insects. Just within the foramen 

 magnum the longitudinal tentorial bars are connected dorsally by a 

 narrow, arched rod, or tentorial bridge (D, E, TB), and shortly 

 before the bridge each bar gives off a slender threadlike branch 

 representing the usual dorsal teiitoricd arm (C, E), which extends 

 forward but disappears before reaching the facial wall of the head. 

 The tentorium of the bee, besides bracing the cranial walls, gives 

 attachment to muscles of the antennae, the maxillae, the labium, the 

 pharynx, and the oral plate of the sucking apparatus. From the 

 deeper part of each posterior tentorial pit there extends into the 

 head cavity a slender hollow rod (D, b), which is attached mesally 



