NERVOUS SYSTEM. VERTEBRATA. 503 



brachial swelling. The shortening of the cord in relation 

 to the vertebral column is indicated by the gradually 

 increasing obliquity of the nerve-roots towards the hinder 

 end. Although there are no functional hind limbs, the 

 posterior part of the cord shows a well marked swelling, due 

 to the great nerve-supply necessary for the tail. There is 

 a strongly developed cauda equina, the component strands 

 of which are more or less tortuous. This condition has 

 been thought to be " due to the great freedom of movement 

 and flexibility possessed by the caudal portion of the 

 animal " (Cunningham, p. 212). 0. C. 1359. 



D. J. Cunningham, Jour. Anat. & Phys., vol. xi. 1877, 

 p. 209. 



D. 792. The spinal cord of a Porpoise (Phocazna plwccena), in- 

 jected. The dura mater has been removed from the dorsal 

 surface. 0. C. 1360. Hunterian. 



D. 793. The cervical portion of the spinal cord of a Dolphin 

 (DelpJiinus tursio) , showing the origins of the eight cervical 

 and first thoracic pairs of nerves. The dura mater has' 

 been removed from the ventral surface, and has been 

 longitudinally divided upon the dorsal surface and reflected 

 to either side to show the underlying membranes. The 

 arachnoid is distinguished by a white bristle inserted 

 between it and the pia. The roots of the first four cervical 

 nerves are very oblique. 0. C. 1361. Hunterian. 



D. 794. A transverse section through the thoracic region of the 

 spinal cord of the same Dolphin, showing on the section 

 surface the central canal and the infolding of the pia mater 

 into the ventral longitudinal h'ssure. The membranes o 

 the cord have been treated as in the preceding specimen. 



0. C. 1362. Hunterian. 



D. 795. Part of the spinal cord of a Piked Whale (Baloenoptera 

 acuto-rostrata) showing the rootlets of the spinal nerve- 

 roots. 0. C. 1363. Hunterian. 



