KESTEVEN OJf THE ANATOMY OF THE SPINAL COED. 393 



is formed of processes of the cells going upwards towards the brain ; 

 that these are united by connective tissue. 



Dr. Stieda divides the cells of the grey matter, in the Pike, into 

 large and small, the former have generally about five processes, the 

 latter only two. He has never seen the processes of the cells on one 

 side of the cord communicate with those of the opposite side. The 

 processes of the cells are traceable to the nerve roots and into the 

 longitudinal fibres. The nuclei of the white and grey substance be- 

 long to the connective tissue. 



III. The Oeigin and Connection of the Nerve Eoots. 



That the posterior roots of the spinal nerves are attached to the 

 posterior columns, and the anterior roots to the anterior columns, 

 only — was the statement made by Mr. Clarke in 1851. This state- 

 ment was repeated by him in 1853, and with the additional statement 

 that the lateral columns are in immediate connection with the spinal 

 accessory. In his last communication to the Eoyal Society, 1858, 

 Mr. Clarke reiterates the same account in opposition to the denial of 

 Stilling, who maintains that a few fibres traverse the posterior part 

 of the antero-lateral columns, having, Mr. Clarke suggests, probably 

 mistaken vessels for nerve-fibres. 



Posterior roots. The bundles which compose these are larger 

 than those of the anterior ; but their component fibrils are mostly 

 finer and more delicate. In a longitudinal section of the cervical 

 enlargement of the cord of a Cat (fig. 5), the bundles are described as 

 being seen to be of tlu'ee kinds. The first kind enter the cord 

 transversely, and pursue a very remarkable course. Each bimdle 

 after traversing the longitudinal fibres of the posterior column, in a 

 compact form and at a right angle, continues in the same direction 

 to a considerable, but variable, depth within the grey substance, dilat- 

 ing and again contracting in a fusiform manner ; it then bends round 

 nearly at a right angle, and rimuing for a considerable distance in a 

 longitudinal direction dowji the cord, sends forward, at short intervals, 

 into the anterior grey substance a number of fibres like those issuing 

 from the roots of plants. 



" The fibres projecting into the anterior grey substance have the 

 following distribution. Part of them form loops with each other 

 within the grey substance, ^particularly near its border ; others extend 

 directly into the anterior white column A, C, and bending round 

 both upwards and downwards, are seen sometimes to re-enter the grey 

 substance and form with each other a series of loops, and sometimes 

 to continue a longitudinal course within the anterior white columns, 

 amongst the fibres of which they become lost. AVhether the latter, also, 

 ultimately form broader loops with corresponding fibres of the grey 

 substance, it is impossible to ascertain. But even if those which ascend 

 in the anterior columns are continued upwards to the brain, one can 

 scarcely avoid inferring that those which descend re-enter the grey 



