134 PATTEN AND REDENBAUGH. [Vol. XVI. 



direction, which throws the cerebral lobes a little downward. 

 One cross-commissure {a.c) anterior to the mouth and four 

 (p.o.c.''^) posterior to the mouth can be seen, from the exterior. 

 Numerous nerves radiate from the sides of the brain. Those 

 going to the appendages bend neurally, giving to the brain a 

 concave appearance upon the neural side and a convex appear- 

 ance upon the haemal side. 



(i) The Fore-Brain. — The fore-brain {f.br.) lies entirely in 

 front of the mouth, and, when the arterial sheath is removed, 

 appears as two convoluted lobes, the cerebral lobes, separated 

 upon the neural side by a deep longitudinal fissure. Upon the 

 haemal side the fore-brain is depressed in the middle line be- 

 tween the enlarged bases of the lateral eye nerves {l.e.n.). 



From the semicircular lobes lying in this depression the 

 median eye nerve (m.ey.n.) arises by four roots. 



The median olfactory nerves [ol.n.) arise from the anterior 

 extremity of the fore-brain, the lateral ones from the middle 

 lobes of the optic ganglia. 



(2) The Mid-Brain or Tween-Brain. — This is represented 

 by the cheliceral or first thoracic neuromere. A typical neuro- 

 mere (Text-fig. 9) in Limulus consists, according to Patten, 

 of a pair of ganglia united across the median line by several 

 cross-commissures {c.c}j ; two pairs of nerves, a neural pair 

 {n.n) supplying the appendages, and a haemal pair (Ji.n.) sup- 

 plying the internal organs and the lateral expansions of the 

 carapace. 



The neural nerves (Text-figs, i and 13; Pis. VI-VIII and 

 X, Figs. 1-3, II, and 12, 7i.n.') arise from the neural side of 

 the brain posterior to the cerebral lobes and pass neurally to 

 the chelicerae. Some small nerves (Text-fig. i, e.pji.), arising 

 near the bases of the neural nerves, supply the tergo-coxal 

 muscles of the chelicerae. 



The haemal nerves (PI. X, Figs. 11 and 12, h.n/) arise from 

 the haemal side of the brain just posterior to the origins of the 

 lateral eye nerves {l.e.n.), and present a very exceptional distri- 

 bution. After fusing with the haemal nerves of the second 

 neuromere they separate again, and, curving around posteriorly, 

 innervate the epidermis upon the neural side of the body out- 



