| OCR Text |
Show 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 faintly 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 iEluroid aquatic Carnivore, Cynogale. In this instance similarity of habit has gone very little way in evolving similarity of structure, tor, in addition to the divergences as to the form of the basis cranii and as to other points which differentiate the iEluroids and Arctoids, the two former exhibit the following divergences:- The iEluroid 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 limb =68*4. ' Cranial length =29-5. Relative length of palate =16'0. Interorbital breadth = 4 4 . Therefore skull much pinched in behind orbits. Muzzle very long. Zygomata very strong. Cranium not very broad posteriorly. Lambdoidal ridge very large. Rather large infraorbital foramen. Nasals long and narrow. Premaxilke slender. Cribriform plate rather narrow. Scapula quadrate. Humerus rounded anteriorly. Inner condyle moderate, and not perforated. An intercondyloid perforation. Radius with no median process to join ulna. Femur considerably larger than humerus. 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. = 509. = 18-8. = 8-5. = 19. Extremely so. Muzzle very short. Rather slender. Very broad posteriorly. Moderate. Infraorbital foramen very large indeed. Nasals short and broad. Premaxilla5 very broad. Cribriform plate rather broad. Anterior margin very convex. Produced into a sharp eye anteriorly. Inner condyle very large and perforated. 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. 1 See I. c. p. 20. |
