THE INDUSIUM OF THE CALLOSUM. 



By Pierre A. Fish, B.S. 



Instructor in Physiology^ Vertebrate Zoology and Neurology, Cornell University. 



The recent papers by Blumenau' and Marchand" on the de- 

 velopment of the callosum have conduced to a much more 

 complete morphological understanding of that important region. 

 Simple as it may appear superficially, there are nevertheless 

 involved questions which may be of the profoundest significance, 

 from a physiological as well as from an anatomical standpoint. 



Perhaps no other part of the human body exemplifies bet- 

 than this the importance of correlating the earlier and later con- 

 ditions of organs and their parts, in order to obtain an adequate 

 and true conception of their structure and function. Embryol- 

 ogy and morphology should go hand in hand — one should sup- 

 plement the other. 



Indiisium griseum is the name applied by Obersteiner^^ 

 to the vestigial layer of the cerebral cortex, existing with greater 

 or less distinctness upon the dorsal surface of the callosum, in 

 many other mammals. 



It has long been known that the apparent dorsal surface of 

 the human callosum does not present a distinct transversely 

 straited appearance. Lancisius''' noted two mesal and two 

 lateral striations passing longitudinally over the dorsum of the 

 callosum. He describes the mesal as tctetcs nervi siuiilitcr medu- 

 llares and the lateral as non ven ncrvi sed liinbi. 



Valentin^ has recognized a delicate remnant of gray sub- 

 stance between the meson and the sUiae lateralcs, which ap- 

 peared to be identical with that of the fasciola. Jastrowitz^ found 

 that the fibers(?) do not lie freely on the dorsum of the callosum, 

 but are imbedded in a layer of nerve cells. Stieda^ observed 

 the indusium in the dog and the rabbit. In the dog he found 

 that the extension from each side projected far enough to meet 

 at the meson, but at this point there were no nerve cells. In 



