No. 421.] SKELETON OF THE HEAD OF INSECTS. 43 
The Tendons of the Extensors of the Head.— These are 
strongly developed in Gryllus; they project into the occipital 
foramen (Fig. 25, ex.A.). 
The Dorsal Apodeme of the Head. — This is also well devel- 
oped in Gryllus (Fig. 25, d.ap.). 
The Lateral Cervical Apodemes.— These have been described 
above (see Fig. 20, af). 
The Mandibular Apodemes. — These also have been described 
above (see Fig. 25, maf). 
In this study of the skeleton of the head our attention has 
been confined almost entirely to representatives of the more 
generalized orders of insects. We have felt that to do so was 
the surest way to gain an idea of the fundamental plan of 
structure. The working out of the ways in which this plan 
has been modified in the more specialized groups of insects 
must be left for the future and perhaps for other workers. 

LIST OF ABBREVIATIONS. 
ac. Antecoxal piece. dg. Leg. 
ant. Antenna. md. Mandible. 
ap. Apodeme. m. em. Maxillary epimeron. 
as. Antennal sclerite. mf. ce field. 
at. Anterior arm of the tentorium. Mx. axilla. 
bt. Body of the tentorium. O. "usen 
C. Clypeus. os. Occular sclerite. 
C: First clypeus. Pg. 
C2 Second clypeus. pl. Pleurite 
cl Cephalic lobes. pr Procephalon 
d. ap. Dorsal a e prs. Præstemum. 
dt. Dorsal arm d i. tentorium. ps. Pharyngeal sclerites. 
em Epimeron. pt. Pesterior arm of the tentorium. 
es. Episternum. S. 
e. su.  Epicranial suture. Sp. Sternellum 
ex. h. Extensors of the head. x Superlingua. 
PF. Front. sp. Spiracle. 
Jb. Frontal plate of the tentorium. z. oe. Tendons of the «esophageal 
G. Gena. muscles. 
Gu. Gula. tr. Ticchantin. 
£. Labrum. : E. Vertex. 
Z. i 2d mx. Second maxillæ or labium. 
Lingua. 
Jf. Lateral field. 
