12 



and the epicranium is obsolete. Hence on this aspect there 

 is no indication of the line where the occiput ends and the 

 epicranium begins. 



Postgenae. — On each side ventrad of the occiput and 

 caudad of the gena is a large sclerite. These form the chief 

 portion of the caudal aspect of the fixed parts of the head 

 and may be termed X\\q postgence. 



The postgense are separated from the epicranium by the 

 narrow ridge which separates the lateral from the caudal 

 aspect of the head ; a continuation of this ridge marks the 

 position of the suture which separates the occiput from the 

 epicranium on each side of the head. 



In many insects the postgenas and the occiput are not separate. As this 

 is the case in the more generalized insects the occiput may be regarded as a 

 detached portion of the postgenae. 



Tentorium. — Observe the remains of the membrane 

 which connected the head with the thorax. It will be seen 

 that the postgenae are connected by a strong part extending 

 from side to side, within the head. This is a part of the in- 

 ternal skeleton of the head or tentorium. 



Make a drawing of the caudal aspect of the head, and name 

 'the parts. 



Review. — The skull of a locust consists of six sclerites ; 

 three of these, the occiput and the two postgena, pertain to the 

 caudal aspect, one, the epicranium, constitutes the greater 

 part of the dorsal, lateral, and cephalic aspects, and two, the 

 clypeus and the labrum, form the ventral portion of the cephal- 

 ic aspect. The epicranium consists of the vertex, the. front 

 and the gence. 



Cervical sclerites. — In the membrane connecting the 

 prothorax with the head there is on each side a pair of scle- 

 rites forming a thickened line from the thorax to the head ; 

 these are the lateral cervical sclerites. In some insects there 

 are also ventral and dorsal cervical sclerites. The lateral 



