20 MR. ST. GEOEGE MIVART ON THE 



Lutra. — Three good figures of the braiu of the Otter are given 

 by Leuret and Grratiolet *, and it is also described and figured 

 by Professor P. Grervais t and by Krueg %. These authors de- 

 scribe and represent the parietal sulcus as greatly broadening 

 out anteriorly, and becoming connected by a " plis de passage" 

 witb the sagittal gyrus. In the specimens I have examined it 

 seems, on the other hand, to be rather the sagittal which is 

 enormously expanded towards its anterior end. The crucial 

 sulcus is placed far back, but shows in front of it an unmis- 

 takable, though faintly marked, " Ursine lozenge." As in TIrsus 

 and certain other forms already mentioned, the anterior limb 

 of tbe Sylvian gyrus is very much narrower than its posterior 

 limb. The Sylvian fissure is very long, and extremely oblique in 

 position. Tbe hippocampal gyrus (according to Krueg) is sepa- 

 rated from the sagittal by the junction of the crucial and calloso- 

 marginal sulci. 



MM. Leuret and Gratiolet justly remark upon the possible 

 deception which may arise as to the cerebral condition of an 

 animal from an inspection of its skull only. The cranium of 

 Lutra would seem to show that it is the hinder part of the brain 

 which is specially enlarged, whereas the fact is that it is the 

 anterior part of the brain which is relatively so augmented in 

 volume. 



JEnhyclra. — A cast of the interior of the skull of the Sea-Otter 

 is figured and described by Professor P. Gervais §. It difiers 

 much from that of Lutra in that the crucial sulcus is placed 

 more forwards, and the " Ursine lozenge " is much more con- 

 spicuous and relatively larger. The cerebrum seems to be very 

 convoluted, the parietal gyrus expanding much anteriorly, and 

 the middle of the sagittal gyrus being longitudinally grooved. 



Thus the Arctoid Carnivora present us witli cerebral cha- 

 racters by which they may be distinguished from the Canidge (or 

 Cynoidea) on tbe one hand, and from the ^luroidea on the 

 other. 



They diff'er from the first in not having four circum- Sylvian 

 gyri, in not having the Sylvian gyrus subdivided, and in not 

 having the posterior limb of the parietal gyrus bifurcating. 



* See I. c. p. 382, pi. vi. f L. c. p. 146, pi. ix. fig. 8. 



t L. c. p. 631, pi. xxxvii. § See l. c. p. 146, pi. vi. fig. 9. 



