408 EXTERNAL ANATOMY OF INSECTS. 



tain us longer, namely, its articulation with the trunk, 

 or rather with its anterior segment, the prothorax. — 

 M. Cuvier makes two principal kinds of articulation of 

 the head upon the prothorax, in one of which the points 

 of contact are solid, and the movement subordinate to 

 the configuration of the parts ; in the other, the articula- 

 tion is ligamentous, the head and the thorax being united 

 and kept together by membranes. 



1. The frst of these kinds of articulation — that by the 

 contact of solid parts — takes place, he says, in four dif- 

 ferent ways. " In the most common conformation, in 

 the part that corresponds to the neck, the head bears 

 one or two smooth tubercles, which receive correspond- 

 ing cavities of the anterior part of the prothorax observ- 

 able in the Lamellicorn and Capricorn beetles. In this 

 case the head can move backwards, and the mouth for- 

 wards and downwards. The second mode of solid arti- 

 culation takes place when the posterior part of the head 

 is rounded, and turns upon its axis in a corresponding 

 cavity of the anterior part of the prothorax ; as may be 

 seen in Curculio, Reduvius, &c. The axis of motion is 

 then at the centre of articulation, and the mouth of the 

 insect moves equally backwards and forwards, upwards 

 and downwards, to right and left. — The third sort of ar- 

 ticulation, by solid surfaces, takes place when the head, 

 truncated posteriorly, and presenting a flat surface, is 

 articulated, sometimes upon a tubercle of the thorax, 

 and sometimes upon another flat and corresponding sur- 

 face, as in almost all the Hymcnoptera and the majority 

 of the Diptera. The disposition of the fourth kind of 

 articulation allows the head only the movement of the 

 angular hinge (le seid mouvcmcnt de charniere angulaire). 



