46 BULLETIN- OF THE LABORATORIES 



which are triangular with a single peripheral process ; third, small cells 

 differing from the outer or first layer in that the cells are more spheri- 

 cal, while the cells of the outer layer are spindle shaped. 



On the ventral surface of the callosum the cornua ammonis are 

 connected by transverse fibres. The gray matter of the lower, or pyri- 

 form lobe fuses directly with that of the striatum, and its superficial 

 cell- layer is composed of cells like that of the peripheral, and these 

 are closely compacted and arranged in a tortuous line. 



The septum pellucidum conforms in structure to that of the cortex. 

 The anterior commissure consists of fibres, a part of which radiate to 

 the striatum, and a larger part to the olfactory lobes. 



The pyriform lobe, or protuberance of the ventral surface of the 

 hemispheres, lacks the inner white, its outer cellular portion fusing di- 

 rectly with that of the corpus striatum. 



The general description above condensed is in nearly every detail 

 applicable to the ground hog so that it will render unnecessary any 

 discussion of the external features Sundry discrepancies and errors 

 in the histological descriptions may be noted by comparison with the 

 following pages. 



A detailed special account of the gross anatomy of Arctomys 

 monax, by one of us, is incorporated beyond ; for the present a brief re- 

 view of current views upon the questions here chiefly discussed may 

 prove a fitting introduction to the descriptions. 



With reference to the cortex the prevailing attitude is one of ag- 

 nosticism, as may be inferred from the following passage frome Raue: 



"If the latest researches of Max Schultze are correct, it 

 appears that the nerve cell is essentially only an enlargement, with 

 nucleus and nucleolus,of the axis-cylinder; that, therefore, it does not 

 represent the beginning, but is merely an intervening expansion of the 

 nerve in its course. The bipolar cell is so to be considered. In the case 

 of the multipolar cells of the spinal narrow, from which, according to 

 Deiter's discovery, one axis-cylinder issues to pass toward the periphery, 

 while many other processes spread in different directions, the cell ap- 

 pears to be an intermediate station for the conveyance of innumerable 

 nerve fibrils from different regions in order to unite and form one axis- 

 cylinder. Even here the axis cylinder cannot be considered as origi- 

 nating within the nerve cell. It is only made up there, like the bulk 

 of a main stream, from numerous tributaries, the source of which no 

 one has yet discovered. The researches of Deiter also made it prob- 



