580 ANATOMY OF VERTEBRATES. 



in Man : in the Gorilla it is the shortest of all the long bones of 

 the limbs : the Human tibia also differs from that of the Gorilla in 

 the more equable diameter of the shaft and more parallel contour 

 of the outer and inner sides, with a considerable reduction of the 

 interosseous space between it and the fibula. The crest descends 

 in Man near the middle of the anterior surface of the shaft, with 

 a slightly sigmoid or wavy course. The lower articular surface 

 is uniformly concave from before backward, and is continued at 

 a less open angle and to a greater extent upon the articular sur- 

 face of the inner malleolus, the articulation with the astragalus 

 being deeper and firmer than in the Gorilla and other apes. The 

 outer or fibular malleolus descends in Man lower and more verti- 

 cally than the inner malleolus, interposing a greater obstacle to 

 lateral inflections of the foot upon the leg than in the Gorilla. The 

 foot is shorter in proportion to the leg, in Man, than in any Qua- 

 drumane, and is so articulated that the sole is directed downward : 

 the tarsus is longer and narrower. The entocuneiform presents a 

 flat, reniform surface, anteriorly, to the base of the hallux. The 

 four outer toes are very slender compared with the innermost ; 

 and their proximal and middle phalanges are very feeble compared 

 with those of the Gorilla : all the five toes have the same direction, 

 forward.^ 



The osseous texture of the Human bones is remarkable for its 

 delicacy and finish : it is exemplified in fig. 402 by longitudinal 

 sections of parts of the three chief bones of the pehdc limb. In 

 the section of the upper end of the femur. A, the outer, compact 

 tissue, a, is extremely thin upon the head of the bone, begins to 

 gain thickness at its under part, and at the corresponding part of 

 the great trochanter, and increases until it forms the wall of the 

 medullary cavity. In the cancellous or reticular tissue forming 

 the substance of the head and neck, a tendency to a radiating dis- 

 position, diverging from the under part of the neck, and favour- 

 able to strength, may be discerned in the principal laminae. In 

 the head of the tibia, B, the compact tissue is also very thin, 

 where it encloses the reticular structure occupying the proximal 

 end, and becomes thicker as that structure is absorbed. In both 

 the tibia and fibula is shown the line indicative of the union of 

 the upper ' epiphysis ' with the ' shaft : ' and in the femur there 

 is a similar indication of the epiphysial condition of the great 

 trochanter. 



The more constant sesamoid bones of the Human skeleton, 



' For the details of a compari&on of the limb-bones of Man with those of the Apes, 

 bee cin". vol v. p. 1, pl^. i.-xiii. 



