The gula (Fig. 49, B _d_, and Fig. 47, _z_) is a piece existing in the middle longitudinally of the under-surface of the head; in front it bears the mentum or the submentum, and extends backwards to the great occipital foramen, but in some Insects the gula is in front very distant from the edge of the buccal cavity. The epicranium forms the larger part of the head, and is consequently most inconstant in size and shape; it usually occupies the larger part of the upper-surface, and is reflected to the under-surface to meet the gula. Sometimes a transverse line exists (Fig. 49, A) dividing the epicranium into two parts, the posterior of which has been called the protocranium; which, however, is not a good term. The epicranium bears the antennae; these organs do not come out between the epicranium and the clypeus, the foramen for their insertion being seated entirely in the epicranium (see Fig. 50). In some Insects there are traces of the epicranium being divided longitudinally along the middle line. When this part is much modified the antennae may appear to be inserted on the lateral portions of the head, or even {94}on its under-side; this arises from extension of some part of the epicranium, as shown in Fig. 49, B, where _h_, the cavity of insertion of the antenna, appears to be situate on the under-surface of the epicranium, the appearance being due to an infolding of an angle of the part. There is always a gap in the back of the head for the passage of the alimentary canal and other organs into the thorax; this opening is called the occipital foramen. Various terms, such as frons, vertex, occiput, temples, and cheeks, have been used for designating areas of the head. The only one of these which is of importance is the gena, and even this can only be defined as the anterior part of the lateral portion of the head-capsule. An extended study of the comparative anatomy of the head-capsule is still a desideratum in entomology. The appendages of the head that are engaged in the operations of feeding are frequently spoken of collectively as the trophi, a term which includes the labrum as well as the true buccal appendages.