158 PATTEN AND REDENBAUGH. [Vol. XVI. 



passes haemally outside of the branchio-thoracic muscles, turns 

 toward the median line anterior to the base of the large enta- 

 pophysis {eiitay^'^^^), and enters the large inter-tergal muscles 

 haemal to the heart. Here it breaks up into anastomosing 

 branches, running forward inside the muscle, and into small 

 fibers which pass toward the median line in the epidermis over 

 the second and third pairs of ostia {ost^^^^) of the heart. A 

 large branch, the pericardial nerve (p.n.), passes posteriorly in 

 the epidermis haemal to the heart and gives recurrent branches 

 to the cardiac nerves of the gill region. 



(c) Integumentary Branches. — The integumentary portion 

 of the chilarial nerve (PI. VI, Fig. i) supplies a large area of the 

 epidermis on the posterior portion of the cephalothorax, includ- 

 ing the posterior angles. A few branches are also distributed 

 to the anterior border of the abdomen. As the lateral expan- 

 sions of the carapace are thin in this region, haemal and neural 

 branches cannot easily be distinguished, but near the median 

 line we find the usual small haemal branch running in the 

 epidermis haemally and toward the median line. 



The integumentary branch of the opercular nerve has a limited 

 area of distribution in the anterior portion of the abdomen. It 

 confines itself to the opercular segment, which is conspicuously 

 marked off by the auricular-shaped processes of the abdominal 

 carapace just posterior to the hinge. A small nerve is given 

 off to the epidermis outside the base of the operculum. 



e. Nerves from the Five Branchial Neuromeres (Text-figs. 



16 and 17). 



The nerves from the five branchial neuromeres are very 

 similar in their distribution. These neuromeres are the most 

 typical and primitive, and all the others may be considered as 

 derived from neuromeres similar to them. Each branchial 

 neuromere (Text-fig. 8) contains a pair of fused ganglia (a.g.) 

 united by cross-commissures, and a pair of haemal and 

 neural nerves. The neural nerves (n.n.) arise from the pos- 

 terior side of the ganglion and innervate the appendage, and 

 the haemal nerves {h.n.) arise from the anterior side and inner- 



