(a) O y to -a rch ltectu re.
(1) A ll th e la y e r s o f th e o p tic tectum p a r tic ip a te t o a c e r ta in e x te n t in th e p rocess o f growth
and development as age advances* but th e s u p e r fic ia l son s (la y w s 1 to 10} grows more markedly than th e deeper zon e, which shows l i t t l e ^ o w th .
(11) m t h i s p rocess o f development th e s iz e o f th e c e l l s , however, does not in crease* I t i s
e s p e c ia lly ev id en t th a t th e s i t e o f th e la r g e /
- 1 6 3 -
la r g e s t e l l a t e s e l l s in th e stratum griseum c e n tr a le (la y e r 11) remains imchanged as development p rogresses w ith advancing âge and i s about 40 U in th e one day o ld ohlok and a t a d u lt age,
( i l l ) The c e l l s are more erowded in th e one day old ch ick than in th e a d u lt, and th e in crea se ' in ^ o w t h o f th e o p tic tectum i s due to an
In crease in th e in te r c e llu la r m a te r ia l, id iich , in mammals, has been termed by
Bauer (*83) "the in te g r a tio n organ", (b) F ib r o -a r c h ite c tu r e ,
As shown by Table 7 m yelin ation has begun in a l l th e la y e r s o f th e o p tic tectum excep t perhaps in l a y ^ s B , 14 and 15 even on th e f i r s t day a fte r hatching» The depth o f s ta in in g o f th e sh ea th s
in iron haem atoxylin p rep aration s g ra d u a lly
in c r e a se s as age advances, and i s always g r e a te s t in th e stratum album c e n tr a le .
An exam ination o f th e s ilV é r p rep aration s in d ic a te s th a t th e r e i s an In crease in th e t o t a l number o f th e f ib r e s o f th e opticum tectum as
age advances, and th a t t h is in crea se i s most marked in th e stratum opticum . Q u a n tita tiv e estim a tio n s have, hOwevtr , n o t been made,
1 6 4 #
M
4
0* Mlogoaooplo 0t>è<ÉTatl6iia * £fti«ieus m eaenoephallôus l a t e r a lis pars d o r sa lis» I* M u lt st3imôtura«
(a ) I t oooupies th s f lo o r o f th e o p tio r s jit r io le through-* out i t s rostro»oau d al ex ta n t and l i e s under cover
o f th e O ptio tectum ,
m / §
- 165 .
(b) I t ojctenda -from- the caudal p eelon o f-- the' po'steplor comraiseur® p o s tr a lly to the, tr o c h le a r n u cleu s
caudally»
(c ) U nlike th e fr o g and the Itsa r d i i t oooupies a raore la t e r a l p o s itio n and does n ot approach th e m iddle lin e to undergo fu sio n w ith i t s fe llo w of th e
o p p o site side*
(d) I t has been sa id to be homologoue w ith the submajamalian toru s B oialcirqularie'î ■■ but s tr u c tu r a lly - i t r e s e t t le s more . tiie mammalian I n fe r io r o o llic u lu s and c o n s is ts
Of an-.oval n u clea r mass and a p erip h eral cap su lar son e,
(o ) Q yto* * arc):îltéctu re»
. (i);,. The n u clea r mass c o n s is t a -c h ie f ly o f s t e l l a t e c e l l s , sm all and la r g e . The la r g e s t e l l a t e c o l l s predom inate in the c e n tr a l area o f the n u claar mass and are lik e th o se o f th e stratum griaeuiri c è n tr a le o f th e o p tic tectum .
B e sid e s( a few pyramidal smd fu siform c e l l s are a ls o p resen t.
The n # :le a r mass la continuous d o r sa lly and v e n tr a lly vfith the stratum griseum p^ri-» ventrlcul^iro o f th e o p tic tectum . Dor s a lly i t
3L66 •-
i s obntinuoua w ith th e p e r iv e n tr lo u la r grey o f th e tegmentum*
( f ) rib ro -a ro h iteo tu re#
( i ) The c e n tr a l nuoiear mass c o n s is ts o f a p lexiform network o f fib r e s th e d en sity o f # tic h i s a l i t t l e g rea ter v e n tr a lly and m edially*
The p erip h eral eap gu lsr «one i s Occupied by th e fib r e s o f th e d iffe r e n t fib r e tr a c ts ¥/faich are r e la te d to t h is n u oleer m ass.
( l i ) The hetwbfh i s oohbihuous w ith th a t o f th e p e r ife n tr io u le r la y e r s o f th e f lo o r o f th e t e h t r ic l e and i s connected w ith th e o p tic tectum through th e d orsal
te cto -b u lb a r tr a c t and th e p e r iv e n tr ic u la r network o f th e la t t e r .
I t i s oontihuous a ls o w ith a sim ila r network Of th e tegmentum and d ecu ssa tes
in th e oonm issura t e c t i . B esid es, i t i s in tim a te ly connected w ith th e nucleus isth m i and th e la t e r a l lem niscus*
1 6 7 ■m