514 



Anniversarnj Meeting, 



[Nov. 30, 



readily conceived that Mr. Clarke's investigations, successful though 

 they have heen, have left not a few intricacies of structure still to be 

 unravelled ; and, in speaking of the advances actually made, it will be 

 sufficient here to indicate the chief points which have either been made 

 known for the first time, or more exactly determined and placed in a 

 clearer light through Mr. Clarke's labours. 



One of the principal subjects of investigation was the grey substance 

 which forms the interior part of the spinal cord. The figure which 

 this part assumes in dififerent regions of the cord has been more 

 exactly described and delineated, and the nature and arrangement of its 

 constituent elements more fully examined and more clearly exposed 

 than heretofore. Two columns or tracts, composed of nerve-cells, and 

 previously undescribed, have been shown to exist in the grey substance 

 through nearly the whole length of the cord, and two others in a 

 shorter extent. Moreover Mr. Clarke was, as we believe, the first to 

 point out that the central canal of the spinal cord is lined with 

 epithelium, and he certainly first explained the true nature of the tissue 

 immediately surrounding the canal, which had previously been mistaken 

 for nervous substance. 



The course and connexions of the fibres of the nerve-roots after they 

 enter the substance of the spinal cord have, as yet, been by no means fully 

 made out ; but Mr. Clarke's investigations have shed considerable light 

 on that obscure point of anatomy, and, amongst other observations of 

 moment, he has shown that a part of .the posterior or sentient roots 

 take, in the first instance, a downward direction — an unlooked-for ana- 

 tomical fact, which was afterwards strikingly shown by Brown- Sequard 

 to be in harm.ony v/ith physiological experiment. 



The structure of the medulla oblongata, and the relation of its seve- 

 ral tracts or divisions to the columns of the spiual cord, as well as the 

 intimate nature of the grey masses which arc there superadded, and 

 their connexion with special sets of fibres and nerve-roots, are ques- 

 tions which have long tried the skill and patience of anatomists, and 

 which have received fresh elucidation from the keen scrutiny and saga- 

 cious interpretation of Mr. Clarke ; and in this branch of his inquiry he 

 has arrived at new facts, and has been able to correct serious errors 

 which had been introduced on respected authority. 



But the researches of Mr. Clarke on the spinal cord have not been 

 confined to its perfected structure ; he has investigated the mode of its 

 development in the foetus; and one of his papers in the Philosophical 

 Transactions contains a minute account of the changes observable in the 

 form and structure of both the white and grey substance at successive 

 stages of development, in man, mammalia, and birds ; also, a descrip- 

 tion of the intimate structure of the intervertebral ganglia, and of the 

 mode of development of the cells and fibres which enter into the for- 

 mation of these difierent parts. 



