114 



ANATOMY OF THE CENTEAL NERVOUS SYSTEM. 



The Tectum mesencephali is practically the ganglion of origin and 

 the terminal ganglion for both of the kinds of fibers mentioned; also for 

 a great number of intratectal association-tracts. It receives, also, an afferent 

 bundle from the Thalamus, and in birds and mammals such a one from the 

 cerebrum. 



In the posterior portion of the midbrain lies, in all animals, a single 

 nucleus, from which fibers joid the deep marrow; this nucleus is called 

 the Corpus quadrigeminum posterius (Fig. 65). In mammals, where the 



Deep marrow (Tr. tecto-l 

 bulb, et spiuales) / 



Corpus quadr. post. 



f. . 'jtfyl~W*^ W^t J ■^ Ganglii 



on isthmi 

 Fillet 

 Central trigeminus tract 



Decussation of the peduncles 



oterior extremity of tlie r 

 nucleus of the trigemim 



Anteriorextremity oftliemotorl ^ \ - ^Tf 



- nus ; U. \ ^ ^ 



Fillet - 

 Med. Tr. tecto-spin. cruc. - 



Fig. 65. — Frontal section through the most posterior portion of 

 the midbrain of a lizard. 



anterior part of the roof remains relatively small, this corp. quad. post, 

 reaches a size almost equal to that of the anterior -bodies. 



In the same manner in the anterior division of the roof there lies im- 

 bedded on either side of the middle line a beautifiilly outlined, roundish 

 nucleus, which, up to the present, has only been found in lower animals, 

 and whose demonstration in mammals has not yet been accomplished: 

 Nucleus prmtedalis. 



The base of the midbrain is formed of those masses of fibers which 

 arise in the forebrain and interbrain and pass the midbrain on their way 



