"WHEEL-BEAEEKS. 293 



wlien tlio mnscnliir parts arc dissolved by potash; 

 and hence I infer the existence of a delicate investi- 

 ture of solid substance similar to that of the teeth, &c., 

 enclosino^ the muscular mass. 



The incus, which cannot be sei)arated from the 

 mallei, thus consists of two portions, corresponding 

 to the rami in Brachioniis, &c., each of which forms 

 the lower part of the quadrantic mass just described. 

 At the ventral extremity they are articulated to a 

 slender fulcrum, which is a little bent downward. 

 The solid framework of each ramus sends off, from its 

 inferior surface, a slender curved process, which is 

 connected with the extremity of the fulcrum. 



The action of this apparatus is as follows : — The 

 ciliary vortices produced by the waves of the coronal 

 disk, pass together through the upper sinus, and are 

 hurled in one stream along the centre of the face, 

 nearly to the projecting chin. Here is placed the 

 orifice of the buccal funnel, a perpendicularly descend- 

 ing tube of considerable width, slightly funnel-shaped 

 at the top, the interior surlace of which is strongly 

 ciliated. It descends straight upon the mastax, over 

 the part where the unci unite. But just above this 

 point there are two valves projecting from the Avails 

 of the tube, also well ciliated. These can be brought 

 into contact, or separated in various degrees, at will, 

 and being very sensitive, they regulate the force of 

 the inflowing current, and doubtless exclude hurtful 

 or uselees substances. The current now flows along 

 the two rami of the incus, as I have alrcad}' described; 

 and, passing between their separated points, descends 

 into the oesophagus, a slender duct opening beneath 

 them, and leading to the digesting stomach. 



