390 THE MECHANICAL FUNCTIONS. 



united to the sternum (s) by means of sternal appendices, 

 which are ossified, and appear as the continuations of the 

 ribs, or as if the ribs were jointed in the middle. 



The sternum is of enormous size, extending over a con- 

 siderable part of the abdomen, and having a large perpendi- 

 cular crest descending, like the keel of a ship, from its lower 

 surface. The object of this great development is to furnish 

 extensive attachment to the large pectoral muscles employed 

 to move the wings, and which, taken together, are generally 

 heavier than the rest of the body. Considered with refe- 

 rence to all the other muscles, and to the weight of the body 

 itself, these pectoral muscles are of enormous strength. The 

 flap of a swan's wing is capable of breaking a man's leg; and 

 a similar blow from an eagle has been known to be instantly 

 fatal. The bat is the only instance, among the mammalia, 

 where the sternum presents this peculiar carinated^ or keel- 

 like shape: and the purpose is evidently the same as in the 

 bird.* 



The scapula is generally a small and slender bone. The 

 Jfcpracoid bone (k) is largely developed, and assumes much of 

 the appearance of a clavicle.t But the real clavicles (c) are 

 united below, where they join the fore part of the sternum, 

 appearing as one bone, which, from its forked shape, has 

 been denominated the furcidar bone. In the fowl it is 

 commonly known by the name of the merry -thought. This 

 bone, placed at the origin of the wings, and stretching from 

 one to the other, is of great importance as constituting a firm 

 basis for their support, and for securing their steadiness of 

 action; and being, at the same time, very elastic, it tends to 



* Notwithstanding the great modification the sternum has received in the 

 bird, when compared with its form in the tortoise and the quadruped, we 

 may still trace the same nine elements entering" into its composition, though 

 developed in very different proportions. 



\ Many have considered this bone as being the clavicle, and have regarded 

 the furcular bone as a new bone, or supplementary clavicle: but all the ana- 

 logies of position and of development are in favour of the views stated in the 

 text. 



