OSSEOUS SYSTEM OF MAMMALIA. 27 



an increase in the comparative length of its internal condyle, otherwise 

 the direction of the tibia would be oblique, which would interfere with 

 the position of the feet, and with freedom of progression. The obli- 

 quity of the shaft, the superior length of its inner compared with its 

 outer condyle, arising from the breadth of the pelvis, and the length 

 of the cervix, combined with the necessity of bringing its lower end 

 perpendicularly under the pelvis, in reference to the secure support of 

 the trunk, are characteristics of the human femur. Its axis, also, coin- 

 cides with the centre of gravity, and its line of direction follows that of 

 the trunk. In all these conditions it displays a strong contrast to that 

 of even the most anthropomorphous Ape ; in which the cervix femoris is 

 comparatively short, the shaft straight, and the two condyles of equal 

 length, the entire bone forming an obtuse angle with the vertebral column, 

 if the latter be perpendicularly raised; which angle, in quadrupedal 

 Mammalia, elevated on the hinder extremities, is necessarily still more 

 acute. 



The human knee, as Camper remarks, is of greater depth than width, 

 while that of the Orang is less deep than wide ; a proof that this animal 

 is not destined to a vertical mode of progression. The extent of the arti- 

 cular surfaces of the knee-joint in Man, affords, also, a more ample basis of 

 support than the extent of the same part in quadrupeds ; at the same time 

 that the leg can be continued perpendicularly from the femur, the whole 

 constituting a firm column beneath the superincumbent weight. The arti- 

 culations, indeed, of the tibia, both with the femur and the foot, are of such 

 a character as not to allow of our ordinary mode of progression being 

 otherwise than vertical. At the ankle, a broad base of support is 

 produced by the great expansion of the tibia and fibula : of these, the 

 former only is articulated to the femur, but the latter concurs with it 

 at the ankle, in forming a sort of mortise, for the reception of the 

 articulating surface of the astragalus, by means of which the super- 

 incumbent weight is thrown on the pedal arch. The ankle, therefore, 

 is mechanically so strong and secure, that, notwithstanding the great 

 weight it has to support, and the mobility with which it is indispensably 

 endowed for the purposes of progression, its dislocation, under ordi- 

 nary circumstances, is almost impossible. 



The foot is placed at a right angle with the leg ; it is prolonged ante- 

 riorly, and that, not by the length of the moveable phalanges of the toes, 

 but by the increase of the tarsus and metatarsus : it is also broader than 

 its analogue in the Ape tribe, generally ; and the thumb, or great toe, 

 placed on the same level with the others, is the longest and strongest 

 of all, and cannot be brought to antagonize with them. The bone of 

 the heel is of great size, particularly at its posterior projection, to which 

 the tendons of the great muscles of the calf are firmly attached. 



