Opt 146 



Optic ganglia. — The two nerve centres from which 

 the optic nerves arise, each is formed of a series 

 of ganglionic masses situated between the 

 compound eyes and the procerebral mass, — 

 the ganglionic plate, external medullary mass, 

 and the internal medullary mass. (Gr. optikos, 

 and ganglion.) 



Optic nerve. — The nerve of the eye, which conveys 

 the impressions of vision to the cerebral 

 ganglion, and which is formed by the fibres of 

 the internal medullary mass, and the proto- 

 cerebrum uniting. (Fr. optique, from Gr. 

 optikos, pertaining to sight, and neuron, a 

 cord.) See Nervi oculorum. 



Optic tract, or trunk. — The optic nerve. (Fr. 

 opAiqite, and L. traho, tractmn, to draw ; or 

 truncus.) 



Optlcon. — The first swelling of the optic tract. 

 (Gr. optikos.) 



Ora. — The broad lateral margin of the prothorax. 

 (L., edge, cable, etc.) 



Orb. — A globe ; a circle. (L. orbis, a circle.) 



Orbicular. — In the form of an orb. (L. orbicularis, 

 from orbis.) 



Orbiculate. — A depressed globe in form, whose 

 horizontal section is circular, and vertical oval ; 

 being in the form of an orb. (L. orbiculatus, 

 from orbis.) 



Orbital.^ — Kelating to the upper border of the eye. 

 (L. orbis, and eo, to go.) 



