i in: QBOAHI 09 i 



( h-ii/mally the optic QeTVC \\iili.-iMiuill lumen, which 



unites the ca\itv <>f tin- optic vehicle \\itlt ill" third \.-ntriel, 

 Ui^r. It i- gradually converted int.. :i .-olid cord, h 



case of most Vertebral produced -imply by a thickening of 



the wall- of tin- -talk. due t. cell proliferat ion. until th.- . 

 obliterated. In Mammal- only tin- larger p< .ri i< .n, t hat uhich adjoins 

 the 1. rain, is metamorphosed in tin- manner: the -mailer part, that 

 which i> united with tin- optic \oidr, i-, on tli*> cont rary. intold. 

 tin- proloiiiration of tlic choroi<l fissure backward tor -oiiif di-tailCC, 

 wh'n-ly tlu vtMitral wall is pressed in against the dor>al. Con- 

 > tin ntly the optic nerve here assumes the form of a groove, in 

 which is imbedded a connen i\ t iur cord uith a Mood- vessel that 

 l>ecoiue> the arteria centralis retime. Hyihe ^rouin^ t< _ 

 the edi^es of the groove, the cord at' I ei'\\ ai'U 1" 



enclo 



For a time the optic nerve consists exc > ln>i\-l\ .t - pi i idle -h a p. -d. 

 radially arranged cells in layers, and reseml>le> in iiv jimM- -M-IK ture 

 the wall of the brain and the optic ve-ide. I (id'ei-ont \ iew> are held 

 citmvniini: its further metamorphoses, anil especially concerniiiL' 

 origin of nerve-til>re> in it. Differences >innlar to those <> 

 the origin of the peripheral ner\ .nv maintained. I "pon this 



point three theories have been l.roui:lit foruard. 



According to the older view, which LIKUKKKI ir. 'he optic 



tihresare uevi'lopi'l in loco by tho elongation of tiie >pindle--haped 

 ivlls. Accoidinu to His. KOU.IKKK, and \V. M i : i.i.i:i:. ..n the con- 

 . raiy, tlie wall f the optic \oicle iurni>hes tlie >u-tentat ive i 

 only, whereas the nerve-fibres grow into it from < '/ her from 



the brain toward theretin" (Hi-. Koi.i ; K 1:1: . or 

 M 1.1.1:1;). The stalk of the optic \ id o>n>titute, according 



to thi> view, (inly a juidin_ \vre -wuld preu 



mim :-.i\vth. When the ingrowth has taken place. 



ihc sn>;eniative cells an-, as K -.riho them, arranged 



radially and so united with one another that they con- 

 delicate framework with lunirit udinally elongated -paces. In the 

 latter ar- :iie snrill luindles of Very tine non-nuclear nerve- 



tihres and numeroii- cells, ai i-anp-d in longitudinal rows, \\hieh 

 likewise l)eloii; to the epithelial BQStentatiVQ ti--ue and help to 

 complete the tre-tle-work. 



The embryonic optic nerve is envelop, -d in a connei ' 

 .-heath, which is .separated, as in the ca-e of the brain and secondary 

 optic cup, into an inner, >oft . \a-cular and an outer compact 



