ITS OUTER SKELETON. 



37 



with a slight inclination backwards towards the mouth, whose 

 front wall it forms. On each side, about halfway between the 

 lateral margin and the middle line, the posterior surface of the 

 labrum is strengthened by a vertical chitinous slip set with 

 large setae. Each of these plates passes above into a ring, from 

 the upper and outer part of which a short lever passes upwards, 

 and gives attachment to a muscle (levator menfi). 



Fig. 14. Top of Head, cp, epicranial plate ; oc, eye ; ye, gena. X 10. 



The top and back of the head are defended by the two 

 epicranial plates, which meet along the middle line, but diverge 

 widely as they descend upon the posterior surface, thus enclosing 

 a large opening, the occipital foramen. Beyond the foramen, 

 they pass still further downwards, their inner edges receding in 

 a sharp curve from the vertical line, and end below in cavities 

 for the articulation of the mandibular condvles.* 



Fig. 15. Side of Head, oc, eye ; ge, gena ; inn, mandible. X 10. 



* One of the few points in which we have to differ from the admirable description 

 of the Cockroach given in Huxley's Comparative Anatomy of Invertebrated 

 Animals, relates to the articulation of the mandible, which is there said to be 

 carried by the gena. 



