I04 



PERIPHERAL NERVES AND GANGLIA. 



The rami from the sixth thoracic, the chUarial, and opercular neuromeres 

 mingle with a plexus of nerves distributed over the longitudinal abdominal muscles j 

 from there branches pass forward, ramifying over the surface of the mesenteron 

 as far as the stomodaeum. 



In the branchial neuromeres, the nerves supplying the longitudinal abdominal 

 muscles and the intestine are separate. The former arise from the anterior side 

 of the haemal nerve root (Fig. 60, Lab.), and the latter from the posterior side. 

 In the more posterior neuromeres, the intestinal branches gradually shift their 

 point of origin from the root of the haemal nerxe to the median margin of the neu- 

 romere. In the branchial segments, the intestinal rami send a small branch to 

 the corresponding hasmo-neural muscle. 



The enteric nerves appear to represent the initial stages of the sympathetic 



^-dac. 



Fig. 79. — Muscles and distribution of nerves in the third leg of Limulus, from the anterior side, i-cox., Coxo- 

 podite, or first joint; 2-bas., basipodite, or second joint; 3-isc., ischiopodite, or third joint; 4-car., mer., fused car- 

 popodite and meropodite, or fourth joint; 5-pro., propodite, or fifth joint; 6~dac., dactylopodite, or sixth joint; apo., 

 apodeme. 



Muscles: 30 and &, Plastro-coxal muscles inserted upon anterior side of entocoxite; 3^ and 3^^, tergo-coxal 

 muscles inserted upon anterior side of entocoxite ; e.2-6, extensors of second to sixth joints; /.2-6, flexors of second 

 to sixth joints ;/.«!, flexor of inner manible. 



Nerves: a.e,n., Anterior ento-coxal nerve; br., brain; e.p.n., external pedal nerve; h., haemal branch of in 

 tegumentary nerve; k.ti.^, haemal nerve; in.n.^, integumentary branch; i.p.n., internal pedal nerve; 7n.e.n., median en- 

 coxal nerve; m.n., mandibular nerves; w., neural branch of integumentary nerve; n.n.^, neural nerve; p.e.n., 

 posterior ento-coxal nerve. 



system of vertebrates. It is a noteworthy fact that in Limulus the anterior cranial 

 nerves are not directly united with the enteric plexus by segmental communicating 

 branches. The most anterior connecting branch that is recognizable belongs to 

 the ninth cranial neuromere, resembling, in this respect, the well known condition 

 in vertebrates. 



The Longitudinal Abdominal Muscles and Nerves. — The longitudinal 

 abdominal muscles arise from the posterior haemal side of the endocranium and 

 pass backward, giving slips to each pair of the abdominal entapophases and to 

 the abdominal endochondrites. (Fig. 75.) 



The muscles are provided with a rich nerve plexus, extending their whole length. 



