u 



1920] Du Porte: Muscular System of Gryllus 17 



I. THE ENDOSKELTON. 



(Figs. 1, 2 and 3). 



The Head (Fig. 2). The well developed tentorium consists 

 of a central plate (T.C.) from which two pairs of processes are 

 given off. The base of the central plate forms the ventral 

 edge of the occipital foramen (P.O.) The central plate lies 

 in a horizontal plane approximately parallel to that passing 

 through the median lines of the pleura. A constriction near 

 the base gives this plate a more or less urn-shaped outline. 

 At each of its apical angles it bears a large triangular anterior 

 plate (T. A.), the base of which is attached to the lower edge 

 of the gena near the base, of the mandible. Immediately 

 behind these processes second and smaller pair arises from the 

 central plate. These are the posterior processes (T. P.) ; they 

 are columnar in form and run obliquely forward and upward^ 

 fusing with the epicranium near the base of the antennae. 

 Between the two anterior processes, the central plate and the 

 epicranium, three foramina are formed, an anterior one (F. A),. 

 through which the oesophagus passes from within the epi- 

 cranium to the mouth, and two lateral foramina (F. L.) through 

 which the crura cerebri and the adductor muscles of the mandi- 

 bles pass. 



Three tuberculate apodemes arise from the epicranium at 

 the edge of the occipital foramen, a median dorsal process 

 (A. M.) and two lateral processes (A. L.) These processes 

 serve for the insertion of certain of the muscles which move 

 the head. 



The Veracervix or Neck. (Fig. 1, Cerv.) There are five 

 paired and one unpaired sclerites which support the cervical 

 membrane and on their inner surfaces serve as points of attach- 

 ment for some of the neck muscles. These are the three inter- 

 sternites (Fig. 1, i.st. 7, 6, e) or ventral cervical sclerites, the 

 second of which is median and unpaired; the large interpleurite 

 (Fig. 1, i.p.) bearing an inward projecting process (ap. ip.) at 

 its anterior end, and the two intertergites (Fig. 1, i.t. a 8z 0) 

 or dorsal sclerites. The form and arrangement of these sclerites 

 may be readily seen by referring to Fig. 1. As will be shown 

 later the interpleurite is the only one of much importance for 

 the attacl;ment of muscles. 



