FORE-GUT OF CORYDALIS CORNUTUS L. 589 



mesh-like arrangement as they pass to their respective points of 

 insertion and origin on the bases of the anterior teeth. 



Behind the anterior bases of the posterior teeth there are no 

 longitudinal muscles till near the end of the gizzard. The longi- 

 tudinal muscles found caudad of this point are the terminating 

 portions* of those extending forward from the mid-gut and lie 

 externally with relation to the circular muscles. When found 

 underlying the circular muscles they are passing to their points of 

 insertion. 



The circular muscles of the gizzard are much increased in the 

 posterior half where the powerful teeth are located. Behind the 

 gizzard they are small and few in number till we reach the oesopha- 

 geal-valve region. This occurs at the beginning of the four longi- 

 tudinal ridges which almost completely close the lumen leading 

 into the mid-gut. Also at this point the longitudinal muscles 

 from the mid-gut pass in large numbers between the caeca and 

 are inserted on the chitinous ridges, the ridges alternating with the 

 caeca. 



From the arrangement and position of the muscles of the giz- 

 zard their action seems apparent. By the contraction of the 

 circular muscles the lumen can be completely closed, thus exercis- 

 ing a crushing and straining action on the enclosed food. The 

 longitudinal muscles, contracting and relaxing at the same time 

 as the circular muscles, would give to the large teeth a grinding 

 action on each other effecting a vigorous trituration of the food. 

 The relaxation of all the muscles combined with the resiliency of 

 the intima and the onward motion of any food in the oesophagus 

 would open the gizzard allowing the entrance of more food. Thus 

 there would be a fairly rhythmic action of the gizzard — contrac- 

 tion and gradual distension following each other. 



The action of the muscles of the oesophageal valve is clear. 

 The circular muscles by their contraction can readily close the 

 lumen, preventing the passage of unbroken food particles or, in 

 connection with the oesophageal valve, regurgitation from the 

 mid-gut; the longitudinal muscles in turn, aided by the resili- 

 ency of the intima, open the lumen thus allowing the onward 

 passage of food from the gizzard. 



