112 TEE BONES. 



more particularly in these two regions that the question of analogies has 

 been resolved in a contradictory manner by anatomists. It would have 

 appeared less complicated had it been studied in a large number of species. 



It has been pretended that the patella and the upper part of the tibia 

 represent the superior extremity of the ulna and radius ; and that the 

 inferior portion of the ulna is represented by the fibula, and the lower part 

 of the radius by that of the tibia. This opinion is erroneous. It is true 

 that in Man the tibia and patella articulate with the femur, as the superior 

 extremity of the ulna and radius responds to the humerus. But in quad- 

 rupeds, whose thoracic members are destined to sustain the weight of the 

 body, this disposition is no longer observed ; the radius is seen to give 

 support to all the humeral surface, just as the tibia receives the femoral 

 surface ; and, besides, the ulna becomes only a simple complement to the 

 elbow articulation, as the fibula does to the femoro-tibial articulation. 



The tibia, therefore, corresponds to the radius, and the fibula to the ulna. 



The olecranon is represented by the supei-ior nucleus of the fibula, and 

 not by the patella. The latter bone is nothing more than a kind of sesamoid, 

 intended to facilitate the action of the extensor muscles of the leg. It 

 might be objected to this comparison that, in the anterior limb, the extensor 

 muscles are attached to the olecranon. But we reply that it matters little 

 where the muscles which move the leg or arm are fixed on one or other 

 of the two bones of these regions, because these bones act conjointly in the 

 movements of flexion and extension. 



Parallel between the hones of the posterior and those of the anterior foot. — 

 The analogy becomes so marked when these two regions are compared, that 

 it is scarcely necessary to allude to it. The tarsal bones are to the posterior 

 limb what the carpals are to the anterior one ; it is even possible to compare, 

 one by one, the several pieces in these regions. The metatarsals are but a 

 repetition of the metacarpals ; while the digital bones are so much alike that 

 it is difScult to distinguish the anterior from the posterior phalanges. 



CHAPTEE III. 



THE BONES IN BIEDS. 



These animals, destined for the most part to sustain themselves in the air, should 

 exhibit in the conformation of their skeleton all the conditions which may favour serial 

 locomotion ; from this arise the differences which distinguish their skeleton from that 

 of mammalia, — differences which will noTf be rapidly traced. 



Veetebkai, Couvmi.— Cervical vertebrsi.~The cervical stalk represents in the bird, 

 as in the mammal, a kind of balancing pole curved like an S, which supports the head, 

 and by its changes of form and direction varies the centre of gravity. When a bird 

 rises in the air and flies rapidly, it lengthens the neck and stretches out the head to 

 carry the centre of gravity forwards. But when it rests on the ground, it makes the 

 balancmg-pole assume the natural and more or less graceful inflection, by throwing the 

 head backwards, and transferring the greater portion of the weight of its body to the 

 columns of support fornied by the posterior members. These displacements of the centre 

 of gravity are executed in birds on a more extensive scale than in mammalia; the 

 vertebral stalk m the former is also longer, lighter, and enjoys an excessive mobilitv. 



^ 7^**'*! *? J°™P°^i'ig it number fourteen in fowU, twelve in the pigeon, fifteen in 

 the d«e/c, and eighteen m the goose ; in the swan twenty-three have been counted -—a 

 curious variety which singularly contrasts with the numerical unity noticed as one of 

 the most remarkable characters in mammalia ! These vertebra? are generally lono-er 

 than m the latter class, and are particujarly distmguished by the configuration of the 



