120 THE CAT. [chap. iv. 



humerus is the larger, while in the femur it is the inner or peroneal 

 one ; (4) that the ulna is the larger bone in the arm, while the 

 fibula is much the smaller in the leg ; (5) that the ulna is the main 

 element of the elbow-joint, while the fibula is excluded from the 

 knee-joint ; (6) that the ulna sends up a very large process (the 

 olecranon) at its proximal end, while the fibula sends up no process 

 at all ; (7) that in the knee-joint there is a patella, while there is 

 no such structure in the elbow-joint ; (8) that the tarsus is grasped 

 between the malleoli, wliile so complete a grasp is not given by the arm- 

 bones to tbe carpus; (9) that there is no bone so large, either absolutely 

 or relatively, in the carpus, as is the os calcis in the tarsus ; (10) 

 that the pollex rests on a saddle-shaped surface, and is slightly 

 separable from the other digits, while the rudimentary hallux rests 

 on a nearly flat surface, and has almost no mobility ; (11) that the 

 metatarsals are long as compared with the metacarpals ; (12) that 

 the tarsus is much longer than is the carpus ; (13) that the hallux 

 is much more rudimentary than is the pollex. 



Though many of these diSierences are incapable of reduction, yet 

 others disappear, and serial homologies become more manifest, 

 if the limbs be placed in that position which is primitive in develop- 

 ment, i.e., if both the knee and elbow be turned outwards. Then 

 the pollex and hallux, and the ulna and tibia, stand in corre- 

 sponding positions in relation to the long axis of the body. 



As to which parts of the os innominatum answer to the several 

 parts of the scapula, different views may be maintained ; but if the 

 lower end of the scapula be rotated outwards, then its subscapular 

 fossa will be seen to answer to the gluteal surface of the ilium, the 

 acromion to the ischium and the coracoid to the pubis, the infra- 

 spinatus and iliac fossoe corresponding. 



Undoubtedly the femur, is the serial homologue of the humerus, 

 and its great trochanter, of the lesser tuberosity ; the radius, of the 

 tibia ; the ulna, of the fibula ; the astragalus, of the scapho-lunar bone ; 

 the ento-cuneifoi'm, of the trapezium; the cuboidcs, of the unciform, 

 and the hallux and other pedal digits are the homologues of the pollex, 

 and the other digits of the hand. 



§ 23. Such being the main facts as to the structure of the internal 

 skeleton, before concluding the subject a few words are needed A^dtli 

 respect to the joints. For, as has been already pointed out, the 

 bones serve as points of attachment for the moving organs or muscles 

 which make use of them as so many levers or fulcra, as the case 

 may be. 



In order that this motion of the bones may take place easily, the 

 interposition is required of certain accessory structui'es between bony 

 surfaces which move one upon the other. Some bones, however, 

 are united by surfaces which join without any such intervention — 

 no motion taking place at the line of junction of such bones. 



Joints may be of three sorts : I. immovable ; II. mixed ; or 

 III. movable. 



The IMMOVAULE joints (synarthroses) may be (1) such as those 



