There is great difficulty in determining pre cisely the functions of the posterior columns of the cord.
Both anatomy and cornpamtive anatomy are opposed to the view which assigns them sensi tive power. In the first place, as already stated, there is no evidence to show that the posterior roots of the spinal nerves are con nected with them ; even Sir C. Bell, who once held that these columns were sensitive because the sensitive roots were connected with them, gave up that view, having satisfied himself that no such connection existed.-I- Secondly, if they were sensitive, it is not unreasonable to expect that they would exhibit an obvious en largement at the situations which correspond to the origins of the largest sensitive nerves; so little, however, is this the case, that the pos terior columns exhibit little or no variation of size throughout their entire course. Thirdly, the researches of the morbid anatomist afford evidence unfavourable to the assignment of the sensitive function to these columns. Cases are on record which show that disease of the pos terior columns does not necessarily destroy sensibility ; that perfect and even acute sensi bility is compatible with total destruction of the posterior columns in some particular region, the posterior roots remaining intact : and others have occurred in which sensibility has been impaired or destroyed, while the posterior co lumns remained perfectly healthy. In a re markable case related by Dr. Webster, there was complete paralysis of motion in the lower extremities, but sensibility remained ; yet there was total destruction of the posterior columns in the lower part of the cervical region. Dr. Webster did me the favour to allow me to examine the spinal cord in this case, and I was struck with the complete solution of continuity of the posterior columns in the region of the neck it was impossible in this case that the nervous force could have travelled along the course of these columns, whether from above downwards, or from below upwards. Such a .atse as this shows distinctly that sensation may be enjoyed in the inferior extremities indepen dently of the posterior columns, and if it does not prove that these columns are not the ordi nary channels through which sensitive impres sions are conveyed to the brain from parts sup plied by spinal nerves, it at least shows that there must be some other channel besides them for the transmission of sensitive impressions.
Other cases to the same purport are on re cord. Alr. Stanley published an account of a case of this kind in the twenty-third volume of the Aledico-Chirurgical Transactions. lie states, " there was no discoverahle impairment of sensation in any part of either limb: on scratching, pricking, and pinching the skin, nowhere was any defect of feeling acknow ledged by the patient. In the upper limbs there existed no defect, either of motion or sensation." There was inability to expel the urine or retain the fmces. The report of the post-mortem appearances in this case is not quite so exact as might be desired. The pos terior half of the cord and the posterior co lumns are spoken of as if synonymous; now it is evident that the posterior half of the cord consists of a great deal more than the posterior columns ; it includes the posterior part of the antero-lateral columns. The record of the case states as follows : " The substance of the cord throughout its posterior half or column, and in its entire length, from the pons to its lower end, had undergone the following changes of colour and consistence; it was of a dark brown colour, extremely soft and tenacious. The substance of the cord through its anterior half and entire length exhibited its natural whiteness and firm consistence ; and on making a longi tudinal section of the cord through its centre, and in the antero-posterior direction, the boun dary line between the healthy and diseased nervous matter was seen to be most exact: it svas a straight and uninterrupted line from the pons to the lower end of the cord. The roots of the spinal nerves were unaltered." Supposing that the posterior columns are the media of sensation to parts supplied by spinal nerves, we can by no means infer that the lesion in this case recorded by Air. Stanley was sufficient to destroy sensation ; it cannot, how ever, be conceded that, if this view were correct, such a lesion could exist without im pairing sensation in some way or other, inas much as the whole of the posterior columns were involved in a notably diseased condition.