250 



THE ANATOMY OF VERTEBRATED ANIMALS. 



interspace between itself and the second, which is often filled 

 up by bony matter. The pollex has two phalanges, and the 

 second of them is, in many birds, pointed, curved, and en- 

 sheathed in a horny claw. The second digit 

 has three phalanges, and the terminal pha- 

 lanx is similarly provided with a claw in sun- 

 dry birds. In the ostrich, both the pollex 

 and the second digit are unguiculate. The 

 third digit never possesses more than one or 

 two phalanges, and is always devoid of a 

 claw. 



It is a singular circumstance that the 

 relative proportions of the humerus and the 

 manus should present the most marked con- 

 trast in two groups of birds, which are alike 

 remarkable for their powers of flight. These 

 are the Swifts and Humming-birds, in which 

 the humerus is short and the manus long ; and 

 the Albatrosses, in which the humerus is long 

 and the manus relatively short. 



In the Penguins, the pollex has no free 

 phalanges, and its metacarpal bone seems to 

 be anchylosed with that of the second digit. 

 The third metacarpal is slender and straight. 

 The bones of the manus are singularly elon- 

 gated and flattened. 



The pelvis of a bird (Fig. 86), is remark- 

 able for the great elongation, both anteriorly 

 Fig. 85.— Theraaras(r); and posteriorly, of the iliac bones {H.), 



which unite with the whole length of the 

 edges of the sacrum ( Sm.) and even extend 

 forward over the posterior ribs of the dor- 

 sal region. Below, each iliac bone forms a 

 wide arch over the upper part of the acetab- 



g\U;Si^eaT|S. ^^1"^ C^^^-), the centre of which ^ is always 



closed by fibrous tissue, so that, in the dry 

 skeleton, the bottom of the acetabulum is perforated by a vride 

 foramen. An articular surface on the ilium, on which the 

 great trochanter of the femur plays, is called the antitroclianter. 

 In all ordinary birds, the ischium (Fig. 86, -?^.), which broad- 

 ens toward its hinder end, extends back, nearly parallel with 

 the hinder part of the ilium, and is united with it by ossifica- 

 tion, posteriorly. The iliosciatic interval is thus converted into 

 a, foramen. The pubis {^Pb.^ enters, by its dorsal or acetabular 



ulna {u) ; radial and 

 ulnar carpal bones (r', 

 -w') ; with the three di- 

 gits (i., ii., iii,), of the 

 right fore-limb of a 

 Fowl. The terminal 

 phalanges of both the 

 first and the second di- 



