COMPARATIVE ANATOMY. 



human subject, which well deserves the 

 name bestowed on it by Aristotle, of the 

 organ of all organs. The great superiori- 

 ty of that most perfect instrument, the hu- 

 man hand, arises from the size and 

 strength of the thumb, which can be 

 brought into a state of opposition to the 

 fingers, and is hence of the greatest use 

 in grasping spherical bodies, in taking up 

 any object in the hand, in giving us a firm 

 hold on whatever we seize ; in short, in 

 a thousand offices, which occur every 

 moment of our lives, and which either 

 could not be accomplished at all, if the 

 thumb were absent, or would require the 

 concurrence of both hands, instead of be- 

 ing done by one only. Hence it has been 

 justly described by Albinus as a second 

 hand, " manus parvamajori adjutrix," de 

 sceleto, p. 465. 



Allthesimiae possess hands; but, even 

 in those which many be most justly stiled 

 anthropomorphous, the thumb is small, 

 short, and weak ; and the other fingers 

 elongated and slender. In others, as 

 some of the cercopitheci, there is no 

 thumb, or at least it is concealed under 

 the integuments; but these animals have 

 a kind of fore-paw, which is of some use 

 in seizing and carrying their food to the 

 mouth, in climbing, &.c. like that of the 

 squirrel. The genus lemur has also a 

 separate thumb. Other animals, which 

 have fingers sufficiently long and movea- 

 ble for seizing and grasping objects, are 

 obliged, by the want of a separate thumb, 

 to hold them by meaus of the two fore- 

 paws ; as the squirrel, rat, opossum, &c. 

 Those which are, moreover, obliged to 

 rest their body on the fore-feet, as the 

 dog and cat, can only hold objects by 

 fixing them between the paw and the 

 ground. Lastly, such as have the fin- 

 gers united by the integuments, or en- 

 closed in hoofs, lose all power of prehen- 

 sion. 



The metacarpus is elongated in those 

 animals, where the toe only touches the 

 ground in standing or walking ; and con- 

 stitutes the part which is commonly call- 

 ed the fore-leg ; as the carpus is termed 

 the knee. 



The number of metacarpal bones is the 

 same with that of the fingers or fore-toes, 

 except in the ruminating animals. Even 

 in these there are two distinct metacar- 

 pal bones, lying close together before 

 birth : the opposed surfaces first become 

 thinner, then are perforated by several 

 openings, and at last disappear ; so that 

 the adult animal has a single cannon 

 bone, possessing a common medullary 

 cavity, internally, and marked on the out- 



side with a slight groove at the place of 

 the original separation. There is there- 

 fore but one metacarpal bone in the adult 

 for the two toes. The structure of the 

 metatarsus is the same. 



The single finger or fore-toe of the 

 horse is composed of the usual three 

 phalanges ; the first, which is articulat- 

 ed to the cannon, is called the pas- 

 tern : the 2d is the coronet ; and the 

 3d the os basis, or coffin bone, on 

 which the hoof rests. There are also 

 two sesamoid bones at the back of the 

 pastern joint; and an additional part, 

 'called the shuttle-bone, connected to the 

 coffin, 



In those animals which have five 

 toes, as the carnivora, 8tc. that which lies 

 on the radial side of the extremity, and 

 is therefore analogous to the thumb, is 

 parallel with the others ; and the animal, 

 consequently, has not the power .of 

 grasping any object. The last phalanx 

 in these supports the nail of the animal ; 

 and sends a process into its cavity. 

 These parts are so connected, that the 

 nail is naturally turned upwards, and not 

 towards the ground : so that its point 

 is not injured in the motions of the 

 animal. The phalanx must be bent, in 

 order to point the nail forwards or down- 

 wards. 



The order of rodentia have generally 

 five toes ; that which corresponds to the 

 thumb being the shortest. 



The elephant has five complete toes ; 

 but they are almost concealed by the 

 thick skin. 



The pig has four toes ; two larger 

 ones, which touch the ground ; and 

 two smaller behind these, which do 

 not reach so far. There is also a bone, 

 which seems to be the rudiment of a 

 thumb. 



The phalanges of the cetacea are flat- 

 tened, not moveable, and joined together 

 in the fin. 



BONES OF THE LOWER EXTREMITY. 



The length of the femur depends 

 on that of the metatarsus ; and it bears 

 an inverse ratio to the length of that 

 part. 



Hence it is very short in the horse, 

 cow, &c. where the same mistakes are 

 commonly committed in naming the parts 

 as in the anterior extremity. 



The proportions of the thigh and leg 

 vary in different animals. The latter part 

 exceeds the former in the human sub- 

 ject ; and the same remark may be made 

 respecting the arm and fore-arm. These 



