THE NERVOUS SYSTEM. 389 



to 0*003 of a line, many of which form loops ; there are, however, in 

 this layer together with these, some of the finest fibrils, measuring 

 0*0004 of a line. Notwithstanding all my endeavors, I have been unable 

 to discover any connection between the nerve-cells and fibres, in the 

 cortical portion of the cerebrum ; but the existence of such a connection 

 would appear to me to be nowhere so probable as here, where the nerve- 

 fibres, especially in the pure gray layer, assume so much the appearance 

 of processes of the cells, as almost to deceive the observer, and where, in 

 any case, they terminate. There are in this situation an immense 

 number of nerve-fibres, so fine and pale that they could scarcely be 

 regarded as such, were they not straighter than the processes, and did 

 they not, particularly when treated with soda, exhibit minute varicosi- 

 ties. If anywhere in the central organs, an origination of nerve-fibres 

 exists here, although it is quite intelligible that it should not yet have 

 been observed, when we consider the delicacies of the structures con- 

 cerned. 



The corpus callosum presents, in the anterior portions of its body 

 above the septum pellucidum, the fornix, and the corpora striata, dull 

 gray streaks, scattered in the white substance, in which the microscope 

 discovers no cells, but only clear vesicles of 0-003-0-004 of a line, with 

 nuclei, in the midst of numerous nerve-tubes, similar to what are met 

 with in certain fasciculi of fibres of the corpus striatum. Besides this, 

 Valentin (" Nervenl.," p. 244) occasionally noticed on the surface of the 

 corpus callosum, between the raphe and the strice obtectce, a delicate 

 gray investment with clear nerve-cells, which appears to be identical 

 with the fasciola cinerea, which is continued into the fascia dentata of the 

 pes hippocampi major (vid. Arnold. " Bemerk," p. 87) ; otherwise the 

 corpus callosum is wholly composed of white medullary substance with 

 parallel nerve-fibres of exactly the same aspect and diameter as those 

 of the medullary substance of the hemispheres. The same may be said, 

 also, of the commissura anterior and fornix, which latter, however, 

 comes in contact with gray substance in very many ways, as in the optic 

 thalamus, from the tuberculum anterius of which its radix descendens 

 arises ; in the corpus mammillare (vid. sup. 116) ; at the commence- 

 ment of the radix ascendens ; in the floor of the third ventricle, to- 

 wards which some delicate fasciculi of the radix ascendens are given off; 

 and at its point of junction with the septum pellucidum, which latter, 

 together with a common thick coat presenting much connective tissue 

 and corpuscula am.ylacea (vid. 118), exhibits numerous plexuses of the 

 finest kind of nerve-fibres and nerve-cells, exactly as does the tuber 

 cinereum. The fibres of the fornix measure, in its white portions 

 0-0008-0-005, mostly 0-002-0-003 of a line; in the optic thalamus (upper 

 part), and in the corpus mammillare^ the fibres are only of the finest sort, 

 measuring 0-0004-0-001 of a line. The cornu ammonis, and the calcar 



