386 



DR. ST. G. MIVART ON THE ARCTOIDEA. [Apr. 21, 



The brain ' is, of course, wide behind, as is the skull which holds 

 it ; its dorsal surface is very complicated, but exhibits a rather 

 faiutly marked Ursine lozenge placed rather far back. The anterior 

 limb of the Sylvian gyrus is very much narrower than its posterior 

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

 crucial and calloso-marginal sulci appear to join. 



As similarity of habit often produces, or coexists with, similarity 

 of structure, thus giving rise to independent resemblances which are 

 no sign of genetic affinity, it may be interesting to compare the 

 structure of the Arctoid aquatic Carnivore, Lutra, with that of the 

 ^luroid aquatic Carnivore, Cynogale. In this instance similarity of 

 habit has gone very little way in evolving similarity of structure, tor, 

 iu addition to the divergences as to the form of the basis cranii and 

 as to other points which differentiate the jEIuroids and Arctoids, 

 the two former exhibit the following divergences : — 



The ^luroid Otter, Cynogale. 



Neck more than a fourth the length 

 of spine from atlas to end of sacrum. 



Tail little more than half such length 

 of spine. 



Humerus and radius together more 

 than one third such length. 



Pectoral limb to spine at 100 =:55'5. 



Pelvic Umb =68'4. 



Cranial length =29'5. 



Relative length of palate = Ifi'O. 



Interorbital breadth =4'1, 



Therefore skull much pinched in be- 

 hind orbits. 



Muzzle very long. 



Zygomata very strong. 



Cranium not very broad posteriorly. 



Lambdoidal ridge very large. 



Eather large infraorbital foramen. 



Nasals long and narrow. 



Premasilhe slendei-. 



Cribriform plate rather narrow. 



Scapula quadrate. 



Humerus rounded anteriorly. 



Inner condyle moderate, and not per- 

 forated. 



An intercondyloid perforation. 



Radius with no median process to join 

 ulna. 



Femur considerably larger than hu- 

 merus. 



Tibia of about the same length as the 

 femur. 



Anterior molars much elongated. 



First upper premolar large. 



First inferior true molar not sectorial. 



Second inferior true molar two thirds 

 the length of the first. 



The Arctoid Otter, Lutra. 



Hardly more than a fifth. 



More than eight tenths. 



Hardly more than one quarter, 



^ 395. 

 = 50-9. 

 = 18-8. 

 = 8-5. 

 = 1-9. 

 Extremely so. 



Muzzle very short. 



Rather slender. 



Very broad posteriorly. 



Moderate. 



Infraorbital foramen very large in- 

 deed. 



Nasals short and broad. 



PremaxilltE very broad. 



Cribriform plate rather broad. 



Anterior margin very convex. 



Produced into a sharp eye anteriorly. 



Inner condyle very large and per- 

 forated. 



No intercondyloid perforation. 



Radius with a median process to join 

 ulna. 



Very slightly so. 



Tibia decidedly larger than femora. 



Not so. 



Very small. 



Sectorial. 



Not half the length of the first. 



See I. c. p. 20. 



