178 PATTEN AND REDENBAUGH. [Vol. XVI. 



thetic, the plexus in the flexors and in the extensors of the 

 telson, and the anterior branches of the segmental cardiac nerves 

 supplying the median inter-tergal muscles, are similar examples. 

 In fact, wherever muscles of different metameres fuse together, 

 we find the nerves supplying them united into longitudinal 

 connectives. The first haemal nerve or lateral nerve is an 

 exceptional case in that it extends through nearly all metameres 

 of the body, but does not communicate with any of the other 

 haemal nerves except the second. 



4. The brain may be divided into four regions : (i) the fore- 

 brain, or cerebral lobes, which is probably formed of three 

 neuromeres, an olfactory, a median eye, and a lateral eye neuro- 

 mere ; (2) the mid-brain, formed of the cheliceral neuromere ; 

 (3) the hind-brain, formed of five thoracic neuromeres, those from 

 the second to the sixth ; and (4) the accessory brain, formed 

 of two neuromeres, the chilarial, or seventh neuromere, and the 

 opercular, or eighth neuromere, both of which were originally 

 abdominal neuromeres. 



5. The neuromeres of the accessory brain region, the 

 chilarial and opercular neuromeres, are more completely united 

 than those in front of or behind them, and some of their nerves 

 wander into other metameres than their own. This fact led 

 Dr. Patten to call the accessory brain the "vagus region." 



The cardiac nerves of these two neuromeres are completely 

 fused and on the haemal side of the body form the pericardial 

 nerve, which extends into the five branchial neuromeres. 



6. In the typical cranial neuromere the neural nerve divides 

 into three groups of branches: (i) the mandibular branches; 

 (2) the ento-coxal branches ; and (3) the pedal branches. The 

 haemal nerve also divides into three branches : (i) the intestinal 

 branch ; (2) the cardiac branch ; and (3) the integumentary 

 branch. 



The ventral cord consists of five branchial neuromeres (those 

 from the ninth to the thirteenth) and three post-branchial neuro- 

 meres (the fourteenth, fifteenth, and sixteenth). 



In the typical abdominal neuromere the neural nerve arises 

 from the posterior side of the ganglion and divides into there 

 branches, one to the anterior and one to the posterior side 



