554 



THE NERVOUS SYSTEM 



(ganglion retince). The bipolar cells of this layer form the per- 

 ipheral neurones of the optic path. Their distal processes termi- 

 nate in relation with the rods and cones ; their central processes 

 are continued into the optic nerve either, as possibly occurs,, with- 



FlG. 414. A SECTION OF THE HUMAN BRAIN STEM, AT THE LEVEL OF THE OPTIC CHIASM. 



C, capsula extrema; Ce, external capsule; Chll, optic chiasm; Ci, internal cap- 

 sule ; CV, claustrum : Cml, lateral nucleus of the mammillary body ; Cmm, medial nu- 

 cleus of same; Coa, anterior commissure; Cospm, supramammillary commissure ; Csth, 

 hypothalamic body of Luys ; Fmp, principal fasciculus of the mammillary body ; Fo, 

 fornix ; yjt?, perforating fibres of the crusta; Frtf, Meynert's bundle; Fu, uncinate fas- 

 ciculus; Ghb, ganglion habenulae; 77, Forel's field ; #7, dorsal part of same; 7777, ven- 

 tral part of same ; *, internal nucleus of the medial ganglion of the mammillary body ; 

 Lml, medial medullary layer of the thalamus ; Narc, arcuate nucleus ; JVc, caudate nu- 

 cleus ; NL, centre median ; Nlv, ventro-lateral nucleus of the thalamus ; Ntg, red nu- 

 cleus; Pp, crusta ; SnS, substantia nigra; St, stria cornea; 8trz, stratum zonale of the 

 corpora quadrigemina ; Tbc, tuber cinereum ; 777, optic tract ; 7Y, tsenia thalarni ; F777, 

 third ventricle ; Zi, zona incerta. Weigert's stain, x 1|. (After Marburg.) 



out interruption, or, as is usually the case, by the interposition of a 

 new set of neurones whose nerve cells form the large ganglion cell 

 layer of the retina (ganglion nervi optici). Neuraxes from these 

 large nerve cells (optic neurones of the second order) penetrate the 

 nerve fibre layer of the retina, enter the optic nerve, decussate in 



