STUDIES ON LIMULUS. 



193 



artery [f.ar.), the anterior portion of the intestine {int.) with proventriculus {prov.) 

 and oesophagus {oe.), and the rectum, or proctodaeum [proc), with the sphincter 

 ani (s.a.) and levator ani {La.), are left in position. 



The muscles are dissected away from the left side of the endocranium {endo.), 

 so that the various parts are exposed to view, viz., anterior cornu {a.cor.), lateral 

 cornu {I.e.), haemal processes {h.pr.), latero-posterior processes {l.p.pr.), posterior 

 process {p-pr.), capsuliginous bars {b.c.'), and the foramina (y.^ andy^^). 



Some of the abdominal endochondrites (a.e.^''^^) with the attached haemo- 

 neural muscles {h.n.tn.^''^*) are also seen. 



To the anterior cornu {a.cor.) of the endocranium are attached three tergo-pro- 

 plastral muscles (A/.w.a-c); to the haemal process {h.pr.), the dorso-lateral plastro- 

 tergal muscles {d.l.p.t.) and the dorso-lateral plastro-entapophysial muscle {d.l.p.e.); 

 from the side of the posterior process a large meso-plastro-entapophysial {m.p.e.) 

 muscle goes to the large entapophysis {enta.^ ^"'^ ^) ; longitudinal abdominal 

 muscles {l.a.tn.) go from the endocranium to each of the abdominal entapophyses 

 {enia.'^'^*) ; and inter-entapophysial muscles {i.e.m.) go from the first entapophysis 

 {enta.i ^"<i ^) to the next four {enta.'^-'^^) . 



Two veno-pericardiac muscles {v.p.771.^ '^"'^ i) are attached to the sides of the 

 endocranium and the bases of the remaining six (z'.p.m.^''^^) are seen amongst the 

 longitudinal abdominal muscles. 



The ventral cord (v.c^ emerges from behind the endocranium and presents to 

 view the abdominal ganglia with the roots of the neural and haemal nerves poste- 

 rior to the eighth neuromere. The neural nerves («.;/.^"") are cut off. The 

 haemal nerves upon the left are cut off, and those upon the right are all concealed 

 from view except the last four {/^.«.""'^), but their bases with the origins of the 

 intestinal nerves are exposed. 



The plexus of intestinal nerves upon the abdominal muscles is in life largely 

 hidden from view within these muscles. All the branches which go to the intes- 

 tine are represented as cut off at the points where they enter the organ. 



The two anterior intestinal nerves (/.«.* and i.n.'') come through the foramina 

 {f.^ andy.''), and these with the next one {i.n.^) join the plexus within the muscles 

 upon the haemal side of the endocranium. From this plexus numerous branches 

 run forward to the anterior part of the intestine. 



In the abdominal region some regularity about the branching of the intestinal 

 nerves has been observed. In the ninth, tenth, and eleventh neuromeres two 

 intestinal branches {a.i.n. 2ind p.i.n.) arise; the anterior one {a.i.n.) joins the plexus 

 in the abdominal muscles ; the posterior one {p.i.n.) gives a branch to the haemo- 

 neural muscle {h.n.in.) of its own neuromere and a branch to the intestine. 



In the twelfth neuromere the posterior branch anastomoses with the plexus in 

 the abdominal muscles, sends one branch to the haemo-neural muscle (/^.;^.w.'^), 

 whence one proceeds to the intestine. It also gives off another posteriorly 

 which anastomoses with a branch from the fourteenth haemal nerve, and then 

 proceeds to the intestine. 



From the thirteenth haemal nerve {h.n.^^) only one intestinal branch (?.«.") 

 arises, and this enters the intestine by two branches. 



From the fourteenth haemal nerve {h.n.^*) upon the left side an intestinal 

 nerve {i.n.^*) arises and, passing a long distance posteriorly, enters the intestine 

 by several branches. From the fourteenth haemal nerve upon the right side three 



