ENCEPHALON IN MAMMALIA. 



79 



46 



processes of the arachnoid called f ligamentum denticulatum,' and 



the nerve-roots. 



204. Encephalon, its primary divisions. The encephalon, or 



brain, of Mammals, 

 like that of lower 

 Vertebrates, Tur- 

 tle, fig. 45 (vol. i., 

 Shark, fig. 187, 

 and Lepidosiren, 

 fig. 186), presents 



four primary Se "- Brain of a Turtle (Chelone), side view. 



merits or divisions, indicated by as many superincumbent, origi- 

 nally vesicular, masses, or pairs of masses ; but consisting, not 

 only of those, but of tracts of the myelencephalic columns from 

 which those masses are successively developed. 



The hindmost division, or 

 6 epencephalon,' fig. 46, c, con- 

 sists of the enlarging parts of 

 the myelencephalic columns, a, 

 called f medulla oblongata,' of 

 the superincumbent mass, c, 

 originally a pair in the human 

 foetus (fig. 47, c), called ( cere- 

 bellum,' and of a transverse 

 commissure of that body, called 

 6 tuber annulare ' or ( pons varolii,' p ; the three parts, so named in 

 anthropotomy, are subordinate 

 elements of one and the same pri- 

 mary division of the encephalon. 1 



The next division includes 

 the parts of the myelencephalic 

 columns which support, and 

 from which are developed, the 

 optic lobes, o : it is the 'mesen- 

 cephalon,' figs. 45, 46 and 47, o. 

 With the columnar elements v j^^^/ K 



are the parts Called the ( fillet,' Brain of human foetus, at four months, side view. 



and ' processus a cerebello ad testes ' in anthropotomy, including the 

 6 third ventricle ' and its prolongations into the vascular appendages 



1 The severance of the 'pons,' and raising it, in association with parts of another 

 segment, to the rank of a distinct primary division as ' mesocephalon,' and the sever- 

 ance of the ' medulla oblongata' from the cerebellum, as a co-equal division, called 

 ' metencephalon,' indicate the warping of the judgment through habitual contem- 

 plation of the characteristically modified and developed parts of the human brain. 



P 



Brain of Opossum 



> side view. 



