PHYLUM ARTHROPODA 



239 



cutting, crushing, and other purposes as in strictly mandibulate 

 types. The maxillae and the labial palpi are folded to form a 

 sheath within which an elongated portion of the labium serves 

 as a lapping tongue. 



Sclerites and Sutures of the Head. — A considerable number of 

 sclerites are fused to form the head capsule. In many instances, 

 the sutures separating the sclerites are visible, and both sutures 

 and sclerites bear definite names. In the generalized insects, 

 as, for example, in the Orthoptera, the epicranial suture (Fig. 

 114) is one of the best and most constant landmarks. This 

 suture originates at the margin of the occipital opening (through 

 which the vicera of the head and thorax are continuous) and 



Epkroinial suiure 

 Gei 



Tenhr. 



Ppst^ei 

 rronf 



Maxilla 

 CiLjpeus 



Labrurn 



Fig. 114. Fig. 115. Fig. 116. 



Figs. 114-116. — Morphology of an insect head. 114, frontal aspect of cock- 

 roach head; 115, lateral aspect; 116, dissected frontal aspect. {Redrawn from 

 Comstock with permission). 



extends as a median suture over the dorsal surface of the head. 

 At its ventral extremity, the epicranial suture bifurcates, and 

 thus its form is that of an inverted Y. Between the arms of the 

 Y, there is an unpaired sclerite, called the front, which in most 

 insects bears the median ocellus. An additional unpaired sclerite 

 ventral to the front is the clypeus. On its ventral border the 

 clypeus is articulated with the labrum or upper lip. 



The several paired sclerites of the head, including the lateral 

 surfaces (Fig. 115) and the parts dorsal to the arms of the epi- 

 cranial suture, constitute what is termed the epicranium. The 

 vertex is just dorsal to the front. It is between the compound 

 eyes and usually bears the paired ocelli. The occiput extends 

 between the vertex and the occipital foramen mentioned above. 

 The genae and the postgenae form the lateral portions or cheeks 

 of the epicranium. A chitinous supporting structure called the 

 tentorium (Fig. 116) is found within the head. This usually 



