EDITOR'S INTRODUCTION. 1 7 



In order to render the following account of the structure of a bird's skeleton intelligible to the 

 non-scientific reader, we have delineated that of the Pigeon, and with this figure before us we shall 

 have but little difficulty in indicating those points with "which it is essential that the reader of the 

 present volume should be intimately acquainted. (See Fig. 12.) 



In the back-bone, or vertebral column, we find three principal regions, each of which will merit 

 distinct notice. 



The cervical region, or that portion belonging to the neck (Fig. 12, b), is exceedingly variable in 

 its proportionate length, and forms the only flexible portion of the spine ; it performs, indeed, the 

 functions of an arm, at the end of which the beak, the chief instrument of prehension, is situated. 

 The number of vertebra entering into the composition of this part of the skeleton is very variable ; in 

 the Swan there are as many as twenty-three, in the Crane nineteen, while in the Sparrow there are 

 only nine. As a general rule, it may be observed that the neck of a bird is never so short as not to 

 be able to reach to every part of the body; in many aquatic species it is remarkably elongated, 

 whether they swim upon the surface by means of webbed or natatory feet, like the Swan, or wade into 

 rivers and marshes, like the Crane or the Heron. Throughout the entire class a very beautiful con- 

 trivance is observable in the S-shaped curvature of this region, the joints of the upper vertebras being 

 so disposed that they will bend fonvards, while in the lower part they can only be bent backwards, 

 thus enabling the bird to lengthen or shorten its neck -with the utmost facility and gracefulness. 



But if flexibility is thus admirably provided for in the cervical region, in the thoracic portion of 

 the skeleton which has to support the framework of the wings, and sustain the efforts of the powerful 

 muscles connected with flight, firmness and rigidity become essential requisites, and, accordingly, in 

 the dorsal region, every means has been employed to prevent those movements which in the neck 

 are so advantageously permitted. The vertebras of this region (Fig. 12, c) are therefore so con- 

 solidated as to be almost immovable ; and, moreover, splints of bone laid along the back materially 

 add to its stability and strength. There are likewise two sets of ribs, one firmly lashed to the back- 

 bone, the other strongly attached to the sides of the sternum ; these dorsal and sternal ribs are 

 moreover united to each other by firm connections, and a thorax is thus formed, possessing sufficient 

 mobility to perform the movements connected with respiration, but still affording a strong basis for 

 muscular action ; nay, still further to strengthen this part of the skeleton, from the hinder margin of 

 each dorsal rib a broad flat plate of bone (Fig. 12, f) is prolonged backwards, so as to overlap the 

 rib next behind, and thus bind the whole together as firmly as possible. 



The sternum or breast-bone (Fig. 12, e) is developed in proportion to the size of the three 

 pectoral muscles subservient to flight, and is prolonged beneath into a deep keel-like projection. In 

 the cursorial races, such as the Ostriches and the Apteryx, whose wings are not available for flying, 

 the keel is entirely wanting. 



Whoever considers the position of the hip-joint in the skeleton of a bird, and reflects how 

 far it is necessarily removed behind the centre of gravity when the bird walks with its body in 

 a horizontal position, will at once perceive that the hinder portion of the spinal column, haring to 

 support the whole weight of the body under the most disadvantageous circumstances, and at the same 

 time to give attachment to the strong and massive muscles that wield the thigh, must be consolidated 

 and strengthened in every possible manner, and that even the slight degree of movement permitted 

 in the region of the back would here be inadmissible. Most of the hinder vertebras are, therefore, 

 solidly conjoined into a single piece (Fig. 12, r, s), sufficiently strong and massive to bear the great 

 strain to which it is continually subjected, leaving only a few of the hindmost pieces (Fig. 12, d) free, 

 upon which the feathers of the tail are supported 



The fore limb of a bird, although used for the purpose of flight, when stripped of tine feathers 



3 



