Geological Society. 140 



After stating various observations which he made on the dislocated 

 eye, the author gives an account of the effects which resulted from 

 section of the optic nerve. The condition of the retina after the 

 operation, was studied during the life of the animal by means of the 

 ophthalmoscope ; and, after death, its structure, as well as that of 

 the optic nerve before and behind the place of section, the chiasma, 

 the optic tracts, and connected part of the brain, was examined 

 with the microscope. 



The elements of the retina, as well as those of Jacob's membrane, 

 were found unaltered fotir months after the time of section. The 

 distal part of the optic nerve (that left in connexion with the eye- 

 ball), examined after the lapse of a month in one case, and of two 

 months in another, was also discovered to be unaltered. On the 

 other hand, the part of the nerve behind or on the central side of 

 the section was invariably disorganized. The section was usually 

 performed on the optic nerve of the right eye, and the disorganized 

 fibres of its central segment could be traced back to the left optic 

 tract, through the chiasma, where they obviously decussated with 

 the sound fibres of the opposite nerve. The right optic tract had 

 undergone no change ; the fibres of the left tract were disorganized 

 as far back as the quadrigeminate bodies, except those running along 

 the posterior or inner border of the tract *, which exception appears 

 to the author to ilvour the opinion that fibres pass along the tracts 

 and commissures from the quadrigeminate bodies of one side to those 

 of the other side, without connecting themselves with the retina. 

 On the other hand, the results of his experiments do not seem to 

 him to countenance the notion of fibres running in the optic nerves 

 from one retina to the other without connexion with the brain, nor 

 the generally received doctrine that part of the fibres of the optic 

 nerve are continuous with the optic tract of the same side ; on the 

 contrary, the whole fibres of the nerve would seem to undergo decus- 

 sation. 



The microscopic characters of the atrophied and disorganized 

 nervous substance are described in the paper ; they were found to 

 differ somewhat in the part of the nerve before and that behind the 

 chiasma, owing no doubt to the different structure of these parts in 

 the sound state. 



The changes produced in the geniculate and quadrigeminal bodies 

 will be communicated in the succeeding part of the paper. ^ 



GEOLOGICAL SOCIETY. 



[Continued from p. 73.] 



June 18, 1856. — Special General Meeting. — Sir C. Lyell, Vice- 

 President, in the Chair. 



It having been announced from the Chair that, in consequence of 

 the lamented decease of Daniel Sharpe, Esq., the late President, the 

 Meeting was called to elect a President and a Member of Council, 

 the Meeting proceeded to ballot and unanimously elected Col. Port- 

 lock, R.E., to the Office of President, and Hugh Fakoner, M.D., 

 F.R.S., as a Member of Council. 



