ACCOMMODATION 



535 







.Accommodation. 



-Pupil. 



Convergence. 



Corp.Quad. 



FIG. 230. Schematic representation of the optic tracts, modified from Fuchs. 



The field of vision common to the two eyes is composed of a right half, G, and a left half, G f . The 

 former corresponds to the left halves I and I,, of the two retina?, the latter to the right halves 

 r and r,. The boundary between the two halves of the retina is formed by the vertical merid- 

 ian. This passes through the fovea centralis, /, in which the line of vision (V) drawn from 

 the point of fixation, F, impinges upon the retina. The optic nerve fibers arising from the 

 right halves, r and r,, of the two retinae (indicated by the dotted line) all pass into the right 

 optic tract, T, while the fibers belonging to the left halves, I and I,, of the two retinae pass 

 into the left optic tract, T,. The fibers of each optic tract for the most part pass to the cortex 

 of the occipital lobe, O.C. ; the smaller portion of them, m, goes to the oculo motor nucleus, K. 

 This nucleus (cf. page 615) consists of a series of partial nuclei, the most anterior of which 

 sends fibers, P, to the sphincter pupillse; the next one sends fibers, A, to the muscle of accom- 

 modation; and the third sends fibers, C, to the converging muscle (internal rectus, i). 



