1 8 CASSELLS BOOK OF BIRDS. 



and quills that, as we have already seen, form the extensive surface of the wing, will be found very 

 much to resemble the human arm in its general arrangement, presenting only such modifications as 

 are required for the performance of its peculiar function. 



The framework of the shoulder consists of three bones (Fig. 12, //, i, /■), named respectively the 

 scapula or shoulder-blade, the clavicle or collar-bone, and the coracoid bone. The scapula (h) is a long 

 and comparatively slender piece placed upon the ribs, and embedded in the muscles, to which it 

 gives attachment. The coracoid bone (k) is the strongest piece of the shoulder ; it supports the 

 wing at one extremity, while at the opposite it is firmly united to the sternum by a broad and massive 

 joint. But the most peculiarly formed part of the shoulder is the furculum, or " merry-thought," as 

 it is usually called (/ :'), consisting of the two collar-bones united, so as to form but a single fork- 

 shaped apparatus, the presence of which materially enlarges and strengthens the shoulder, without 

 unnecessarily adding to the weight. It is by the union of the three last-mentioned bones that a place 

 is made for the socket of the shoulder, with which the wing is more immediately connected. 



The skeleton of the wing presents the bone of the arm, called the humerus (Fig. 12, /), and the 

 two bones of the fore-arm, named respectively the radius (m) and the ulna, or cubit («). The wrist, 

 or carpus, consists of two bones (V 0), and the metacarpus (/) is likewise made up of two pieces ■ 

 these, with two, or sometimes three, rudimental fingers (/>' q q), complete the framework of the wing. 

 The largest finger consists of two, or sometimes of three joints ; a second offers but a single joint • 

 and the third, when present, is a mere appendage to the carpus, representing a sort of apology 

 for a thumb. 



The bones of the leg likewise exhibit the same parts as exist in the human skeleton, but modified. 

 The thigh, or femur (Fig. 1 2, /), is a short and strong bone, to which succeeds the leg, consisting of 

 two bones (u), named the tibia and the fibula, but the latter is generally very imperfectly developed. 

 That part which is commonly considered to be the leg consists of the bones of the ankle and a part 

 of the foot (the tarsal and metatarsal bones) consolidated into a single piece, called by anatomists the 

 tarso-metatarsal bone, but known to ornithologists as the tarsus (x). At the lower extremity of the 

 tarsus are three joints that support the three front toes (z, z), while a fourth toe (technically called 

 the hallux) (y), which is directed backwards, is attached to it by the intervention of a small 

 accessory piece. In the gallinaceous order there exists a bony spur, considered by some as repre- 

 senting a fifth toe. 



In order to facilitate the description of a bird, it is usual for the ornithologist to consider its 

 exterior as being mapped out into sundry regions (see Fig. 13), to each of which has been assigned 

 a definite and appropriate name ; with the names of these regions, and their precise application, it is 

 requisite that the reader should be intimately acquainted. 



A bird, like any other vertebrate animal, is divisible into the head, the body, and the limbs ; 

 under one or other of which divisions all subordinate parts may be classed. 



The head consists of the skull and the bill, and is joined to the body by the neck. Commencing 

 with the bill, we see that it is composed of two pieces, corresponding to the jaws of quadrupeds ; that 

 which is above is called the upper mandible (Fig. 13, a ), that which represents the under jaw is called 

 the lenver mandible (*). The upper mandible contains the nostrils ( 3 ) ; its highest part is called the 

 admen or ridge ( 4 ), while the corresponding ridge of the lower mandible is called the gonys or keel ("). 



The lateral edges of the mandibles which meet when the bill is closed are called the margins. 

 In some birds the margins of the upper mandible fold over those of the lower, while in others the 

 edges meet ; when this is the case, the line of junction between the two is called the commissure ( 3 ). 



In many birds the upper mandible is continued far back over the forehead, and there dilated, so 

 as to form a casque or helmet. In rapacious birds and parrots there is a belt of soft naked skin at the 



