686 ME. F. G. PARSONS ON THE [Nov. 20, 



He Cowper's glands. The penis is 4 inches long, and has embedded 

 in the dorsum of the glans a triangular os penis, into the base of 

 which the tendons of the levatores penis are inserted. 



The Nervous System. 



The Brain of Atherura (figs. 5, 6), when viewed from above, differs 

 very much in its general appearance from the brains of other Por- 

 cupines. Beddard says ' that " the Hystricidae form a perfectly 

 natural family. Their brain is characterized by its peculiar shape, 

 rounded in front, and by the fact that the convolutions for the 

 most part are transverse and not longitudinal in direction." This 

 description, although it is true for every other Porcupine I have 

 seen, unfortunately would not give a good idea of the brain of 

 Atherura, for in this animal the frontal part of the cerebral 

 hemispheres is quite narrow and the transverse width increases 

 to nearly the posterior end. At the posterior end of the central 

 longitudinal fissure the hemispheres form a deep notch, in which 

 the corpora quadrigemina would be exposed were it not for the 

 great development of the anterior part of the central lobe of the 

 cerebellum. Two fissures are marked, but not deeply ; they are 

 the posterior part of the longitudinal and the Sylvian. The Sylvian 

 fissure does not reach the rhinal fissure below. 



The convolutions and fissures of the brain of Atherura are less 

 well marked than those of Hystrix, but better than those of 

 Erethizon or, apparently, Sphingurus. On the base of the brain 

 the chief points of interest are, the large size of the tuber cinereum, 

 from which the pituitary body depends, and the great development 

 of the external arcuate fibres, which run just behind the pons to 

 join the anterior pyramids at right angles. The same points are 

 present in Hystrix and, according to Mivart's figures 2 , in Ere- 

 thizon. 



In a sagittal section of the brain, the chief point that attracts 

 attention is the peculiar funnel-shape of the aqueduct of Sylvius ; 

 this is of very small calibre where it leaves the third ventricle, but 

 rapidly dilates so that the posterior end of the lamina quadrigemina 

 which forms its roof, and on which the corpora quadrigemina are 

 situated, is tilted up. 



The Spinal Nerves. 



Owing to injuries inflicted on the head in removing the brain 

 and tongue before the animal came into my possession, I was 

 unable to make a complete dissection of the cranial nerves. I have 

 therefore contented myself with a description of the nerves 

 supplying the extremities. 



1 P.Z.S. 1892, p. 596. 

 8 P.Z.S. 1882, p. 278. 



