EXTERNAL ANATOMY OF INSECTS. 407 
tain us longer, namely, its articulation with the trunk, 
or rather with its anterior segment, the prothorax.— 
M. Cuvier makes ¢wo 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 L., 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 Hymenoptera 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 seul mouvement de charniere angulaire). 
