DIPTERA 



781 



The postgentB. — See page 39 . 



The ptilinum. — See page 776. 



The transverse impression. — -See cheek-groves. 



The tormce. — -A sclerite situated between the clypeus and the labrum in the 

 more speciaHzed Diptera. It is composed of two sclerites which belong to the 

 lateral portions of the epipharynx and are internal in the more generalized in- 

 sects; but they become exposed and united on the middle line in the more special- 

 ized Diptera. In such cases the tormae are sometimes incorrectly termed the 

 clypeus. See Peterson ('16 p. 19). 



The vertex. — {a) The term vertex, as defined by Kirby (Kirby and Spencet 

 1 8 15- 1 826), is the dorsal portion of the epicranium; or, more specifically, that 

 portion which is next the front and between the compound eyes (Fig. 998, v. v. v.) 

 (b) This term is often applied merely to the top of the head. 



Fig. 999. — Diagram illustrating the terms 

 applied by writers on chsetotaxy to the 

 areas of the head: a. /. antennal fossa; 

 b, bucca; E, eye; Fa, face; Fr, the so- 

 called front; f.v, frontal vitta; g, the so- 

 called gena; g.p, genovertical plate; v, 

 vibrissa; v. r, vibrissal ridge. 



Fig. 1000. — Cephalic bristles: fa, fa- 

 cial, /r, frontal; /. 0., fronto-orbital; 

 g. 0, greater ocellar; /. o, lesser ocel- 

 lar; ve, vertical; vi, vibrissee. 



The vertical triangle. — See the ocellar plate. 



The vibrissal angles. — Two prominences at the lower ends of the vibrissal 

 ridges upon which are borne the vibrissEe. 



The vibrissal ridges. — Two ridges, one on each side, inside the arms of the 

 frontal suture, constituting the lateral boundaries of the antennal fossa, and 

 bearing the vibrissae (Fig. 999, v. r). These are also termed the facialia or facial 

 ridges. 



THE CEPHALIC BRISTLES 



The ascending frontal bristles. — See frontal bristles. 



The beard. — A clothing of hair borne by the lower part of the so-called occiput 

 and on the buccae. 



The cilia of the posterior orbit. — A row of bristles along the posterior orbit of 

 the eye. 



