THE BONES IN SI EDS. 117 



early period, and are usually absent in the first and last ribs. They concur in an 

 efficacious manner to increase the solidity of the thorax. 



The costal cartilages in mammalia are in birds often transformed into veritable 

 inferior ribs, joined to the superior ribs by a diarthrodial articulation (Fig. 73, i). These 

 pieces are long and strong, and all terminate at their lower extremity by a double 

 facet which articulates with the lateral border of the sternum ; they are nearly always 

 absent in the two first ribs. It is not rare to see the last united to the one before it, 

 instead of passing directly to the sternum; in which case it comports itself like the 

 asternal ribs of the mammalia. 



ANTERIOR MEMBERS. Shoulder-bone. The shoulder comprises: a scapula, a par- 

 ticular bone named the coracoid by Cuvier ; and a clavicle, which forms, in coalescing 

 with that of the opposite side, a single bone called the fork (furculum), or os furculare. 

 The scapula is narrow, elongated, and falciform, and shows no trace of a spine. Its 

 anterior extremity only forms a portion of the glenoid cavity, and is united by means of 

 a fibro-cartilage with the fork of the coracoid bone. The latter is so named because it 

 represents the coracoid process of mammals, and is a long piismatic bone, directed 

 obliquely from above downwards, and before to behind. Its superior extremity is often 

 fused with the scapula, and united at an acute angle with that bone to form a portion of 

 the articular cavity which receives the head of the humerus. Its inferior extremity is 

 flattened from before to behind, and responds by a diarthrodial articulation to the 

 anterior border of the sternum. The coracoid is long in birds which fly slowly ; it is, on 

 the contrary, short, thick, and therefore very solid in quick flyers. The fork is a single 

 bone, shaped like a V or U, situated at the base of the two wings, in front of the trunk, 

 and in an oblique direction downwards and backwards. The two branches which form 

 it represent the clavicles ; they meet and are united at their inferior extremities, where 

 they describe a curvilinear angle more or less open, attached to the brisket by means of 

 a membranous ligament. Their superior extremity rests within, and opposite to the 

 glenoid cavity, against the scapula and coracoid, forming with these bones a remarkable 

 foramen, through which passes the tendon of the elevator muscle of the wing (Fig. 73, 

 A, 4, B, 6). The fork plays the part of an elastic spring, whose office it is to prevent the 

 wings coming towards each other during contraction of the depressor muscles. The 

 conformation of this bone is, therefore, like the sternum, related to the extent and power of 

 flight ; and for this reason it is that, in swift flyers, the two branches of the furculum are 

 thick, solid, widely separated, and curved like a U ; while in those which fly heavily and 

 with difficulty, these branches are thin and weak, and joined at an acute angle. The 

 latter formation greatly diminishes its strength, and lessens, in a singular manner, 

 the reactionary power of the bony arch it represents. 



Bone of the arm. The humerus offers an articular oval-shaped head, and an air- 

 opening placed beneath this eminence. It is long in Palmipedes, ordinarily so in the 

 Gattinacx proper, and very short in Pigeons. 



Bones of the fore-arm. The radius is much less voluminous than the ulna. The 

 latter lias an extremely short olecranon ; and the two bones are separated from one 

 another in their middle part to meet again at their extremities, where they are united 

 by ligamentous bands in such a way as to render the movements of pronation and 

 supination impossible. This mode of fastening, which nevertheless does not prevent the two 

 bones from gliding slightly on each other in the direction of their length, has been wisely 

 adopted by nature in order that the wing might strike the air, like an oar, by its inferior 

 face ; otherwise, the resistance of the aerial medium would make these two bones pivot, 

 and cause the wing to present itself to the air in a wrong direction. 



Bones of the carpus. These are only two, and are distinguished by the names of 

 radius and ulna, in consequence of their corresponding more particularly to these bones 

 in other animals. 



Bones of the metacarpus. These also number only two, and are separated at their 

 middle portion, to be consolidated at their extremities. 



Bones of the digital region. The wing of a bird is composed of three digits. One 

 of them, which resembles the thumb and forms the basis of the false wing, is composed 

 of a single styloid-shaped phalanx, articulated at the base of a small particular process 

 belonging to the superior extremity of the largest metacarpal bone. The largest digit 

 comprises two phalanges which succeed the last bone. The third digit is represented by 

 a small rudimentary phalanx, which corresponds to the inferior extremity of the small 

 metacarpal bone, and lies beside the first phalanx of the large digit in the closest manner. 

 It is well to remark that the hand and the fore-arm are longer in proportion to the 

 quality of flight ; those two regions of the wing, for example, are very short in Gallinaceous 

 Birds. 



POSTERIOR MEMBERS. Coxa or os iliac. This is a voluminous and very solid piece, 

 11 



