4 Journal ok Comparative Neurology. 



After the manuscript was completed and about to be sent 

 to the printer the excellent paper of Houser on the neurones 

 of the selachian brain came into my hands. I have added brief 

 comments upon such parts of this paper as touch upon matters 

 treated in the present paper. It is unfortunate that Professor 

 Houser has not treated of the fiber tracts, and has given neither 

 general figures nor a description of the nerve roots by which to 

 identify the sensory centers in the medulla. 



II. General Description. 



The gross internal anatomy of the brain as it may be made 

 out from a series of cross sections is given here in order to make 

 clear the description of the minute structure which follows. 

 The external form is shown in Fig. i, and the figures in VVied- 

 ersheim's textbook will apply to the brain of Lampetra, with 

 the exception of the nerve roots. There seems to be a great 

 difference in curvature in different individuals. Compare F'ig- 

 ures I and 2, both of which are from brains hardened iti situ. 

 This has made it difficult to bring general sketches like that in 

 Fig. 30 into agreement with transverse sections. No attempt 

 has been made to do this. 



The dorso-ventral flattening of the spinal cord and the cor- 

 responding lorm of the grey matter have been described by 

 several autliors. (Cf. K(">lliker, '96, Fig. 425). In the grey 

 matter large cells are found in two places. Just dorsal to the 

 central cavity are the dorsal or giant cells arranged somewhat 

 irregularly in pairs. At either lateral extremity of grey matter 

 are the motor cells. The remainder of the grey is made up of 

 smaller cells which include the cells corresponding to the dorsal 

 horns of other vertebrates, and the tract and commissural cells. 

 In the white matter there are a large number of very thick 

 fibers, the AIiillerian fibers. About eight of these form a 

 median ventral group beneath .the grey matter on either side, 

 while many others of varying thickness are scattered in the 

 lateral and dorso-lateral parts of the white matter. The median 

 dorsal part of the white matter, bounded laterall)' by the dorsal 



