THE BRAIN OF THE HEDGEHOG. 447 



cusps are remarkably sharp and pointed, and the outer sur- 

 face of the postero-extemal one alone is somewhat inflected. 



In the lower jaw, the con-esponding molars are each 

 marked, as in most Lemurs, by two transverse ridges. In 

 front of the anterior ridge is a basal prolongation of the 

 tooth, on to which a curved ridge is continued inwards and 

 forwards from the anterior principal ridge, giving rise to 

 an imperfect crescent with its convexity outwards. 



According to Rousseau there are twenty -four milk teeth, 



i. -— d.m. — 7, which fall out seven weeks after bii-th. 



4*4 1*1 



The brain of the Hedgehog is remarkable for its low 

 organization. The olfactory lobes are singularly large, and 

 are wholly uncovered by the cerebral hemispheres ; which, on 

 the other hand, do not extend back sufficiently far to hide 

 any part of the cerebellum. Indeed they hardly cover the 

 corpora quadi'igemina. Only a single shallow longitudinal 

 sulcus marks the upper and outer surface of each hemisphere. 

 On the under surface, a rounded elevation corresponds 

 with the base of each corpus striatum. Behind this, another 

 elevation represents the end of the uncinate gyrus and the 

 termination of the hippocampus major; and therefore 

 answers, in a manner, to the temporal lobe. The inner face 

 of the hemisphere presents neither convoliition nor sulcus, 

 except behind and below, where a very broad depression fol- 

 lows the contour of the fissure of Bichat and the fornix, and 

 represents the dentate sulcus. Above, this sulcxis ends be- 

 hind the posterior margin of the corpus callosum. The 

 latter is remarkably short, and directed obliquely backwards 

 and upwards. It has no genu, and the pre-commissural fibres 

 of the ventricular wall spread out, beneath its anterior 

 end, upon the face of the hemisphere. The j^art of the 

 corpus callosum which answers to the hjra is very thick in 

 proportion, and is inclined at an acute angle to the rest. 



In a transverse section, the corpus callosum is seen to be 

 very thin, and to curve upwards and outwards into the 

 roof of the ventricular cavity. The inner walls of the 

 lateral ventricles, which answer to the septum lucidum, are 



