On the Spinal Cord of the Porpoise. 



445 



The authors considered it probable that much information might be 

 obtained by the careful study of the cell groups in the spinal cord of 

 a mammal differing markedly in its musculature from man, and as no 

 previous observations on similar lines had been made in the same 

 fulness on the spinal cord of any of the Cetacea, they describe the 

 results of an examination of the cell groups in each segment of the 

 cord of a member of this class, Phoccena communis. The investigation 

 was carried out by obtaining a very recently captured specimen and 

 at once preserving its tissues by injecting into its blood-vessels a 

 solution of formalin, a method which has the advantage of preserving 

 the natural configuration of the enlargements of the cord. A number 

 of sections were prepared for the microscope by different methods 

 from each segment of the whole cord, and typical sections were 

 selected and photographed. 



The principal features in which the musculature of the porpoise 

 differs from that of man are the almost entire absence of a hind limb, 

 the reduced musculature of the upper limb, and the possession of a 

 large and flexible tail acted upon by powerful muscles, with some 

 other differences noted in the text. 



The segments of the cord giving origin to the nerves supplying 

 these parts were compared with corresponding segments of the human 

 cord. The groups of motor cells were found to be clearly differentiated 

 from one another, and striking changes were found to occur in the 

 shape of the grey matter and in the cell-groups as we passed from one 

 segment of the cord to another, pointing clearly to a connection 

 between the character of the part supplied with motor nerves from 

 any segment, e.g., limb, trunk muscles, genital muscles, — and the 

 arrangement of the anterior horn cells in that segment. 



The area of the grey matter and of the different columns of white 

 matter was also determined at each segment. 



The authors also describe some hitherto unrecorded features in the 

 minute structure of the cord of this animal, especially the position of 

 the nucleus of the spinal accessory nerve, and a detached mass of 

 grey matter, probably corresponding to the vesicular column of Clark, 

 in the lumbo-sacral region of the cord. 



VOL. LXXI. 



