MACROMYELON OF MAMMALIA. 81 



tinned into the ' rhinencephalon,' as shown in fig. 46, d. So 

 that all the essential parts of a primary encephalic division, viz. 

 the columnar as ( cms rhinencephali,' the superimposed mass, and 

 the cavity exemplifying the nature of the olfactory bulb as a 

 c primary vesicle ' of the brain, are present. 



205. Macromyelon.- -The epencephalon consists of the ma- 

 cromyelon and cerebellum. The term ( macromyelon ' is not 

 exactly the equivalent of the ( medulla oblongata ' of anthropo- 

 tomy, the authorities in that department of anatomy having ap- 

 plied the phrase in different senses. With Willis, 1 it included the 

 part of the brain beneath the cerebellum and cerebral hemispheres, 

 * all that substance,' e.g., which reaches from the cavity of the 

 callous body and conjuncture in the basis of the head to the hole 

 at the hinder part where the same substance, being further con- 

 tinued, ends in the f spinal marrow.' With Vieussens, 2 the ( oblong 

 marrow ' included the columns of the neural axis between the 

 4 spinal marrow ' and the ' cerebral hemispheres,' with the ( crura 

 cerebri ' and their ganglionic enlargements, called ' optic thalami,' 

 and ' corpora striata.' Winslow 3 defines the ' medulla oblongata ' 

 as the medullary basis common to both cerebrum and cerebellum. 

 Haller 4 restricts the 'medulla oblongata' to the intracranial 

 myelonal columns, as far as the ( pons varolii.' Rolando 5 prefers 

 the older view of its extent. Chaussier, 6 ao*ain, distinguishes 



7 O O 



the portions of the intracranial columns crossed by the transverse 

 commissural fibres of the cerebellum as a primary division of the 

 brain, under the name ' mesocephale ; ' and this term has been 

 extended by Todd 7 to include the f corpora quadrigemina ' with 

 the f processus cerebelli ad testes,' and part of the floor of the 

 fourth ventricle. 



But the developement of the human brain and its several stages, 

 represented by the conditions at which it is arrested in lower 

 vertebrates, show that the transverse commissural fibres which 

 cross or decussate with the intracranial myelonal columns, whether 

 under the name of ' pons,' or ( trapezoid bodies,' or ' arciform 

 fibres,' are subordinate adjuncts to other parts, chiefly the cere- 

 bellum ; while the distinct and superimposed masses called ( cor- 

 pora quadrigemina ' include the true correlatives of the cerebrum 

 and cerebellum, as primary vesicles of the brain. 



By ( macromyelon,' therefore, I signify the intracranial prolon- 

 gations of the myelonal columns as far forward as their emergence 

 from the ' pons,' or cerebellar commissure : in this tract they are 



1 xxi". p. 5. 2 xxir'. 3 xxiii". 4 xxnii". 



3 i.". 6 xxvi". r xxvii". p. 084. 



VOL. III. G 



