THE TENTORIUM 



49 



nected with those of the trunk. It is very distinct in Hydrous 

 and most Coleoptera, and in some, the Staphylinidse, Carabidse, and 

 Silphidae is constricted and extended backwards so as to form a com- 

 plete neck." (See also p. 51.) 



The tentorium. - - The walls of 

 the head are supported or braced 

 within by two beams or endostern- 

 ites passing inwards, and forming 

 a solid chitinous process or loop 

 which extends in the cockroach 

 downwards and forwards from. 

 the lower edge of the occipital 

 foramen. " In front it gives off 

 two long crura or props, which 

 pass to the ginglymus, and are 

 reflected thence upon the inner 

 surface of the clypeus, ascending 

 as high as the antennary socket, 

 round which they form a kind of 

 rim." (Miall and Denny.) The 

 oesophagus passes upwards be- 

 tween its anterior crura, the long 

 flexor of the mandible lies on 

 each side of the central plate; 

 the supracesophageal ganglion 

 rests on the plate above, and the 

 suboesophageal ganglion lies be- 



low it, the nerve Cords which lal in f posteriores ; u, tentorium; w, kniina- 



orbitales ; a 1 , os trans versum ; y, articulating cav- 

 ity for the mandible; s, os hypopharyngeum. 



After Newport. 



unite the two passing through 

 the circular aperture. (Miall and 

 Denny.) In Coleoptera (Hy- 

 drous) it protects the nervous 

 cord which passes under it. 

 (Newport, Fig. 32, M.) 



In Anabrus the tentorium is V- 

 shaped, the two arms originating 

 on each side of the base of the clypeus next to the base of each mandi- 

 ble (the origin being indicated by two small foramina partly concealed 

 externally and passing inwards and backwards and uniting just before 

 reaching the posterior edge of the large occipital foramen (Fig. 33). 



Flo m _ Interior fllld npper 8nd under sur . 



FIG. 33. Posterior view of head of Anabrus : 

 t. tentiirium. .Jnuti'l del. 



