COMPARATIVE ANATOMY. 



seem to deviate from the human struc- 

 ture. 



Whenever an animal of one class re- 

 sembles those ot'u different order in the 

 form and use of any part, we may be as- 

 sured that this resemblance is only in ex- 

 ternals, and that it does not affect the 

 number and arrangement of the bones. 

 Thus the bat has a kind of wings; but an 

 attentive examination will prove, that 

 these are really hands, with the phalanges 

 of the fingers elongated. The dolphin, 

 porpoise, and other cetacea, seem to pos- 

 sess fins consisting of a single piece. But 

 we find under the integuments of the fin- 

 like members, all the bones of an ante- 

 rior extremity, flattened in their form, 

 and hardly susceptible of any motion 

 on each other. We can recognise very 

 clearly the scapula, humerus, bones of 

 the fore-arm, and a hand consisting of 

 five fingers; the same parts, in short, 

 which form the anterior extremity of 

 other mammalia. See Tyson's "Anato- 

 my of a Porpoise," fig. 10 and 11 : also 

 Blasii " Anatomia Animalium," tab. 51, 

 fig. 3, 4. 



The fore-feet of the sea-otter, seal, wal- 

 rus, and manati, form the connecting 

 link between the anterior extremities of 

 ether mammalia, and the pectoral fins 

 of the whale kind. The bones are so 

 aovered and connected by integuments, 

 as to constitute a part adapted for 

 the purposes of swimming : but they 

 are much more developed than in the 

 latter animals, and have free motion on 

 each other. 



The cold-blooded quadrupeds bear 

 great analogy in the four component parts, 

 and in the general structure of their ante- 

 rior extremities, to the warm-blooded 

 ones. See Caldesi's " Observations on the 

 Turtle," tab. 3, fig. 1, 4, 5. 



The bones of the wings of birds have a 

 considerable and unexpected resemblance 

 to those of the fore-feet of the mamma- 

 lia. And the fin-like anterior member of 

 the penguin contains, within the integu- 

 ments, the same bones as the wings of 

 other birds. 



The clavicle supports the anterior ex. 

 tremity, and maintains the shouldevat its 

 proper distance from the front of the 

 trunk. It exists, therefore, in all such 

 animals as make much use of these mem- 

 bers, whether for the purpose of climb- 

 ing, digging, swimming 1 , or flying. It lias, 

 indeed, been supposed to be confined to 

 Linnaeus's order Primates (in which he 

 includes man, the quadrumanous ani- 

 m,als, and bats.) It ^rill he found in the 



squirrel and beaver, who use their front 

 extremities for the purpose of holding 

 objects, rather than for that of supporting 

 the body : in the mole, who employs 

 them for digging, &c. &c. Many other 

 animals have in its place an analogous 

 small bone, merely connected to the mus- 

 cles, and called, by Vicq d'Azyr, os clavi- 

 culare, to distinguish it from the more 

 perfect clavicle. This is the case with 

 most of the ferae, and some glires. It does 

 Dot exist, on the contrary, in such as Use 

 their fore-feet merely for the purpose of 

 progression, since these limbs must be 

 brought more forwards on the chest, that 

 they may support that part, by being 

 placed perpendicularly under it. In the 

 genera, which hold an intermediate rank 

 between these, which do not enjoy such 

 an extensive utility* of the fore feet as the 

 first division of animals, and are not so 

 limited in their employment as the se- 

 cond, the clavicular bones, or imperfect 

 clavicles, exist. 



In ruminating animals, and in the 

 horse, the metacarpus consists of a sin- 

 gle bone, called the cannon bone, which 

 is very long when compared with that of 

 man. The humerus becomes shorter, it) 

 proportion as the metacarpus is elongat- 

 ed ; so that in animals which have a can- 

 non bone, the os humeri hardly extends 

 beyond the trunk. Hence the mistakes 

 which are made in common language, by 

 calling the carpus of the horse his fore- 

 knee, Sec. 



The radius forms the chief bone of the- 

 fore-arm in the mammalia, generally 

 speaking; the ulna is a small slender 

 bone, terminating short of the wrist in a 

 point, and often consolidated with the ra- 

 dius, as in the horse and ruminating ani- 

 mals. A few genera, which have great 

 and free use of their anterior extremity, 

 have the power of promition and supina- 

 tion. But this power diminishes, as the 

 fore-feet are used more for the purpose of 

 supporting the body in standing, and in 

 progression. In this case, indeed, the ex* 

 tremity may be said to be constantly ia 

 the prone position, as the back of the 

 carpus and toes is turned forwards. 



The lower end of the ulna is larger than 

 that of the radius in the elephant ; but 

 this circumstance occurs in no other in- 

 stance. 



The radius and ulna exist in the seal, 

 manati, and whales, but ia a flattened 

 form. 



Several genera of mammalia possess a 

 hand; but it is much less complete, and 

 consequently less useful than that of the 



