394 



actions of muscles, would lead us to suppose that the fibres of the 

 motor nerves are continuous with those of the cerebellum ; but hi- 

 therto no observations have been made which prove the existence of 

 this connexion ; and it is the object of the author, in this paper, to- 

 establish, by a more careful examination of the anatomical structure 

 of this part of the nervous system, such continuity of fibres between 

 the anterior columns of the spinal cord and the cerebellum. The 

 corpora pyramidalia have been hitherto considered as formed by the 

 entire mass of the anterior, or motor columns of the spinal cord; but 

 the author shows that not more than one half of the anterior columns 

 enters into the composition of these bodies : and that another portion, 

 which he terms the antero-laieral column, when traced on each side 

 in its progress upwards, is found to cross the cord below the corporal 

 olivaria, forming, after mutual decussation, the surface of the corpora 

 restiformia ; and ultimately being continuous with the cerebellum. 

 These fibres are particularly distinct in the medulla oblongata of the 

 sheep and of the horse. The author conceives that the olfice of the 

 antero-lateral columns is to minister to the involuntary? as well as to 

 the voluntary movements: that the facial nerve arises from' both the 

 voluntary and involuntary tracts ; and that the pneumogastric nerve 

 arises both from the involuntary and the sensory tracts-. 



June 9, 1836. 



FRANCIS BAILY, Esq., V.P. and Treasurer, in the Chair. 



" Discussion of the Magnetical Observations made by Captain 

 Back, R.N , during his late Arctic Expedition. By Samuel Hunter 

 Christie, Esq., M.A., F.R.5. 



The author, having been consulted by Captain Back, previous to 

 the departure of the latter, in 1833, with the expedition for the relief 

 of Captain Ross, respecting the nature of the magnetical observa- 

 tions which it might be desirable to make in the regions he was abouts 

 to visit, and considering that, with a view to the attainment of the 

 principal object of the expedition, the greatest economy of time in 

 making these observations was of the first importance, limited his 

 suggestions, in the first instance, to the methods proper to be em- 

 ployed for determining the direction and the dip of the needle, but 

 more especially the latter. Captain Back, immediately on his return, 

 placed all his magnetical observations at the disposal of Mr. Christie, 

 who having since completed their reduction, gives, in the present 

 paper, the results of his labours. 



The first part of the paper relates to the observations of the Dip of 

 the magnetic needle. With a view to economize as much as possible 

 the time consumed in making each observation, the process of invert- 

 ing the poles of the needle, which is usually resorted to in each in- 

 stance, was here dispensed with. But in order that the dip may be 

 determined independently of this operation, it is necessary not only 

 that the position of the centre of gravity of the needle employed should 

 be ascertained, but that it should be permanent. In giving an account 

 of the observations made to verify this condition, the author com- 



