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with tile librt's of the neuroglia cells, which arc located upon the outer surface 

 of the inner ^'ranular layer. The libres of the optic nerve i)ass inwaid vertically 

 to the inner plexus, and in the outer plexus each bears a brush of sh(.)rt straight 

 processes. 



The medulla contains inultiiiolar , or bi]iolar cells of four types: — ''giant", 

 intermediate, small centripetal and small centrifugal cells. The dendrites of the 

 centrifugal and of the small and intermediate centripetal cells are distributed 

 in the medulla: those of the giant centripetal cells are unusually irregular 

 (knobbed), and are distributed to all parts of the ganglion, but are more numerous 

 in the inner plexus. The neurites of the centripetal cells pass toward, and probably 

 into, the optic tract, while those of the centrifugal cells go outward to the 

 outer and inner plexuses. 



A small ga,nglion , somewhat larger than a pin-head , is situated on the 

 anterior and dorsal side of the o])tic tract. This is the "ganglion pedunculi" 

 and seems to be connected with the pleural ganglion alone and only by a few 

 fibres. All its cells are small and their nuclei are separated from one another 

 only by a distance equal to the diameter of a single nucleus. 



The pedal ganglion lies in the concavity of the pedal process of the skull 

 below the oesophagus and above the pedal artery. Its upper surface on each side 

 of the oesophagus is continuous wath the pleural ganglion and is separated from 

 the visceral ganglion by a septum thru which a large number of iibres pass. 

 The pedo-propedal connectives arise from the ventral end of the pedal ganglion 

 and pass forward a short distance to the propedal ganglion. 



The following nerves arise from the pedal ganglia. — 



A. Nerves of special sense. 



1. Two eristic nerves. Each arises from the back end of the pedal ganglion 

 and , as it enters the cartilage of the skull , divides into two branches , 

 one of w^hich innervates the ventral ti-ansverse portion of the crista , 

 and the other the remainder of the crista. The fibres of this nerve 

 are unusually large and stain differentially so that they can be readily 

 traced for some distance in the ganglion. The fibres pass along the 

 surface of the ganglion tor perhaps half its length and then turn inward 

 and form at least a partial chiasma. The fibres have not been traced 

 beyond the chiasma. 



2. A pair of macular nerves. Each arises from the back end of the ganglion 

 some distance inward from the roots of the preceding nerve. It passes 

 immediately into the cartilage and , as it passes thru it to the statocyst, 



