51 



The optic nerves. — These arise caudad of the origins of 

 the antennal nerves. Determine the number of divisions of 

 each optic nerve. 



The crura cerebri. — These are the two, large cords, one on 

 each side, connecting the supraoesophageal ganglia with the 

 suboesophageal ganglion, and forming with these ganglia the 

 nervous collar of the oesophagus. (The singular form of 

 crura is crus.) 



The vagus nerve. — Just cephalad of the supraoesophageal 

 ganglia there is a minute ganglion, the frontal ganglion; 

 this is connected by an arching nerve on each side with the 

 crura cerebri ; from the frontal ganglion there extends ceph- 

 alad a small, branching nerve ; from the frontal ganglion 

 there also extend two nerves which pass caudad ; one of 

 these extends to the commissure connecting the supra- 

 oesophageal ganglia ; the other passes between the supra- 

 oesophageal ganglia and the oesophagus, and ventrad of the 

 aorta (which is usually turned to one side in opening the 

 specimen as this one is opened), to a minute ganglion on the 

 middle line of the oesophagus, caudad of the supraoesopha- 

 geal ganglia. From. this minute ganglion two nerves extend, 

 one on each side, to the sides of the alimentary canal, which 

 they follow to the proventriculus, where they divide into 

 many branches. This system of nerves and ganglia is 

 termed the vagus nerve. 



The suboesophageal ganglion. — This is the large ganglion on 

 the meson, ventrad of the oesophagus. From it two large 

 cords pass caudad to the first thoracic ganglia. 



From the suboesophageal ganglia nerves extend to the labi- 

 um, the maxillae, the mandibles, and to other parts of the head. 

 The beginning students who are taking a short course in ento- 

 mology need not trace out these nerves. Other students may 

 use as a work of reference a paper on this subject by Dr. 

 William C. Krauss, published in "/Vyr//^," vol. IV., pp. 179-184. 



