I^S PATTEN AND REDENBAUGH. [Vol. XVI. 



the chelicerae. He regarded these buds as probably olfactory 

 in function and called the nerves supplying them the olfactory 

 nerves. 



The median olfactory nerve (Pis. VI-VIII, Figs. 1-3, 

 m.ol.n., ol.n) arises from the anterior extremity of the fore-brain 

 in the median line, by two roots, one from each of the cerebral 

 lobes, and passes directly forward beneath the skin to the olfac- 

 tory organs {ol.or.). The proximal end is composed of a mixture 

 of nerve fibers and small ganglion cells which arise, according 

 to Patten, as early outgrowths of the cerebral hemispheres. 

 " The distal end divides into many diverging branches, which 

 can be followed by means of a hand lens to the posterior edge 

 of the olfactory organ ; they there begin to anastomose, and 

 form a dense plexus underlying the olfactory region, but a 

 considerable number of fibers extend beyond the olfactory 

 region to the neighboring ectoderm. The lateral olfactory 

 nerves (Pis. VI-VIII, Figs. 1-3, ol.n., r.ol.n., l.ol.n.) arise 

 apparently from the anterior part of the brain, but in sections 

 one can follow their roots to the ventral surface into the middle 

 lobe of the optic ganglia. In the adult the proximal ends 

 of the nerves consist of coarse transparent nerve tubes 

 and masses of very large ganglion cells. Their distal extremi- 

 ties also contain many clusters of large ganglion cells. The 

 nerve terminates abruptly just beneath the cuticle on the 

 lateral edge of the olfactory organ. The lateral olfactory nerve 

 is accompanied by a large blood vessel that divides into numer- 

 ous branches, supplying the tissues in front of the olfactory 

 organ ; small nerve filaments accompany some of these blood 

 vessels, and probably supply the ectoderm in the same region. 

 Some larger nerve branches leave the median border of the 

 lateral nerves a little distance back of the olfactory organ, and 

 mingle with the plexus formed by the median nerve " (Patten). 



(2) Median Eye Nerves. — Owen described two median eye 

 nerves, but other authorities have found but one. The median 

 eye nerve (Pis. VI-IX, Figs. 1-3 and 5, m.ey.n) apparently 

 arises from the anterior border of the fore-brain, but examina- 

 tion of sections shows that it arises by four roots from the 

 semicircular lobes upon the haemal side of the fore-brain. It 



