The r a d ia l f ib r e s , appeeriy s in g ly , permeate a l l th e la y e rs and are continuous p erip h era lly w ith la y e r 2 , and c e n tr a lly w ith la y e r 7 .
Layer 7a ‘
i l l ty p es o f f ib r e s - tra n sv ers e , o b liq u e, and r a d ia l - ere p resen t in t h is la y e r . The fib r e s are
arranged in a p lexifb r® maniier thrbugh th e sca ttered c e l l s end n u c le i o f th e la y e r . The tra n sv erse and ob liq u e
f ib r e s appear in sm all bundles and merge w ith th e se o f la y e r 8 , The r a d ia l f ib r e s en ter th e s u p e r fic ia l as w e ll as th e deeper la y e r s .
Layer 8;..
This la y e r , to o , c o n s is ts o f tra n sv erse, ob liqu e and
r a d ia l f ib r e s . The fib r e s show more d is t in c t ly in th e se I p rep aration s than in th e iron#*haemetoxylln o n es. The
tra n sv erse end ob liq u e fib r e s outnumber th e r a d ia l and c o n s titu te th e c h a r a c te r istlb fea tu re o f t h is la y e r .
They appear in sm all cbmjpaot bundles o f d iffe r e n t len g th s extending even in to la y er 7 . D o rsa lly and r o s t r a lly th ey d ecu ssate /
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d ecu ssate in the d orsal part of th e p o ste rio r commissure (Fig* 13)} fu r th e r cau d ally th ey do so in the d ecu ssa tio t e c t i m esencephali (F ig , 1 0 ), V en traily they en ter th e tegmentum form ing the d orsal and the v en tra l tocto-bull»c.r and te c to -te © n e n ta l tr a c ts and d ecussate in the d orsal and the v e n tr a l teg n e n ta l d ecu ssation s (F ig s , 14, 1 5 ). B esid es th ey en ter th e toru s sem icircu la ris* oculomotor n u cleu s, and nucleus Isthm i o f the same s id e . Further they e s ta b lis h communication vrf.th the fa s c ic u lu s lo n g - it u d in a lis m e d ia lis.
The r a d ia l f ib r e s are very few in number and appear s in g ly . P er ip h era lly they en ter the s u p e r f ic ia l la y e r s , d escrib ed alread y, and c e n tr a lly they jo in ,th e plexiform network o f the deeper p e r iv e n tr ic u la r la y e r .
Layers 9 to 13;
The plexiform network o f fin e f ib r e s , contained in th ese la y e r s , i s aggregated in to two very narrow zones i . e . la y e r s 10 and 12 , which desnarcate th e e n tir e c e llu la r and n u clear zone in to th ree in d e fin ite la y e r s i , e . la y e r s 9 , 11, and 13* described alread y. P er ip h era lly th e n et work i s invaded by the r a d ia l fib r e s o f la y e r 8 , and i s continuous c e n tr a lly w ith tdie network o f la y e r 14.
D orsally i t i s continuous w ith i t s fe llo w o f th e o p p osite s id e /
■ . I
- 7 1 - '
s id e through th e d o rsa l p art o f th e p o ste r io r commissure r o s t r a lly and th e roof o f the o p tic tectum ca u d a lly ,
V en tra ily , however, i t en ters th e tegmentum and i s
continuous w ith th e network o f th e toru s sem icircU la ris [Fig. 1 0 ).
Laver 14;
■ ; ■ I
T his la y e r resem b les la y e r s 10 and 12. LaVer 15;
No fib r e i s p resen t in t h is layer* ft:.)
a- % B. TORUS, SBMIOIRCULARIS.
The toru s s e m ic ir c u la r is , as alread y s ta te d , l i e s in th e f lo o r o f the o p tic v e n tr ic le . I t forms a prominent b u lgin g o f the m edial p art o f th e f lo o r o f th e v e n tr ic le a t the le v e l o f th e oculom otor nucleus (F ig . 1 4 ).
O pposite the caudal p art o f t h is n u cleu s i t fu s e s in th e median plane w ith i t s fe llo w o f th e o p p o site s id e
sep ara tin g com p letely th e o p tic v e n tr ic le from the aque d u ct, The fu sed t o r i thus form th e roof o f th e aqueduct.
The o p tic v e n t r ic le , however, does not extend to th e caudal 4" lim it o f the to r u s, but sto p s sh ort a l i t t l e caudauL to th e
s i t e /
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s i t e o f fu sio n o f the two t o r i. Throughout i t s e n tir e