270 



KV'^ENIXGS AT THE illCKOSCOPE. 



The 2)rincii3al or two stout rami, resting on what ap- 

 pears, when yon look at the back or belly of the ani- 

 mal, to be a slender foot-stallv {fulcrum). But when 

 you get a lateral view the foot-stalk is seen to be only 

 the edge of a thin plate, to the upper edge of which 

 are jointed the rami, in such a manner that they can 

 open and close, like the blades of a pair of shears. 

 Each ramus is a thick, three-sided piece, with the upper 

 side hollow, and the inner flat, and in contact w^ith that 

 of its fellow, in a state of repose. The uncus of each 

 malleus fiills into the concavity of its corresponding 

 ramus, and is fastened to it by a stout triangular mus- 

 cle, which allows some freedom of motion. 



Many muscles are inserted into various parts of 

 these oi-gans, and into the walls of the mastax, which 

 impart various and complex motions to all the parts. 



Thus, as we have seen, they are 

 adapted to the various func- 

 tions of mouth-organs, those of 

 grasping, holding, bruising, and 

 chewing food. 



The mallei correspond with 

 the mandibles of Insects ; and 

 the rami of the incus with the 

 maxillic ; while the walls of 

 the mastax with the two edges 

 of its orifice correspond Avitli 

 the mouth, with its labrum and labium. 



It is true we are somewhat startled to find a moutli 

 placed ftir down within the cavity of the breast ; but 

 there are other forms in this class, some of which I may 

 be able to show you, where the mastax has essentially 

 the same structure, in which it is placed at the front 



MOUTH OF BKACIIIONUS. 



