408 EXTERNAL ANATOMY OF INSECTS. 
The only examples at present known are in some species 
of Attelabus. 'The head of these insects terminates be- 
hind in a round tubercle, received in a corresponding 
cavity of the thorax: the lower margin of this cavity has 
a notch, and permits the movement of the head only in 
one direction*.” 
2. The second kind of articulation, the ligamentous, 
he affirms takes place only in orthopterous and some 
neuropterous insects : ‘The head in this kind of articula- 
tion is only impeded in its movements towards the back, 
because it is stopped there by the advance of the pro- 
thorax; but below it is quite free. The membranes or 
ligaments extend from the circuit of the occipital cavity 
to that of the anterior part of the prothorax, which gives 
a great extent to the movement >.” 
When I consider the well-deserved celebrity of the 
great author whose words I have here quoted, and the 
great and useful light that the genius and learning which 
conducted his patient labours and researches have thrown 
over every department of comparative anatomy,—a sci- 
ence he may be almost said to have founded,—I feel the 
most intire reluctance to differ in any thing from an au- 
thority so justly venerable to all lovers of that interesting 
study. But, however great my diffidence and hesitation 
to express an opinion at all opposed to his, the interests 
of truth and science require that I should state those 
particulars in which my own observations, made upon a 
careful examination of various insects of every Order, 
have led to results in some respects different from the 
above. ‘* Aliquando bonus dormitat Homerus ;” and 
* Anat. Compar, i, 445—. » [bid. 447. 
