322 



NORMAL HISTOLOGY. 



the bodies ; in man and apes this layer is unusually well developed, 

 reaching a thickness of 30-40 t* ; the interlacing fibres, derived 

 from the optic tract, form a lamina rather than distinctly-grouped 

 bundles. 



2. The stratum cinereum, a cap-like mass of gray matter, em- 

 bracing the subjacent optic fibres, and containing numerous nerve- 

 cells of varying size, the larger ones occupying the deeper parts of 

 the layer. 



3. The stratum opticum, consisting of the continuation of the 

 preceding gray matter, through which extend the bundles of optic 

 nerve-fibres entering by the superior brachium ; posteriorly the fibres 

 are fine, while anteriorly they become robust to take part in the 



FIG. 347. 



Section across superior corpora quadrigemina and adjacent part of thalamus : i, 

 Sylvian aqueduct ; gr, gray matter of aqueduct ; c.q.s., quadrigeminal body, con- 

 sisting of, /, stratum lemnisci, o, stratum opticum, r, stratum cinereum ; Th, thala- 

 mus (its pulvmar) ; c.g.i., c.g.e., internal and external geniculate bodies ; br.s ., br.i., 

 superior and inferior brachia ; _/", upper fillet ; /./., posterior longitudinal bundle ; r, 

 raphe ; ///, third nerve ; .///, its nucleus; l.p.p., posterior perforated space; s.n., 

 substantia nigra, above this tegmentum with circular nucleus; cr, crusta ; //, optic 

 tract; M, medulla of hemisphere; H.C., nucleus caudatus ; st, stria terminalis. 

 (After Quain-Meynert ) 



constitution of the optic tract. Among the profusely distributed 

 nerve-cells are elements of considerable size whose axis-cylinder 

 processes extend largely within the underlying zone. 



4. The stratum lemnisci, including gray matter as well as nerve- 

 fibres, many of the latter being continuations of tracts connecting 

 lower levels. 



The geniculate bodies, lateral and mesial, are closely associated 



