49 



points with respect to flight. The bones of the skull differ from those found 

 in the skulls of Mammals in the complexity of the lower jaw, and in its being 

 attached to the skuU by the interposition of another bone called the quadrate- 

 bone, instead of being attached by a condyle. 



The backbone of birds is remarkable from the anchylosis or union which 

 takes place in the lumbar and dorsal regions of the back, so that in birds the 

 neck and tail vertebrse are the only moveable ones. This immobility of the 

 dorsal and lumbar vertebras is for the purpose of giving fii'mer and steadier 

 points of attachments to ribs, and to avoid the danger of dislocation during the 

 movement of the wings. The hip bones are long and thin, and the pubic bones 

 do not join to form an arch as in mammals. 



The thigh bones are short but very strong and cylindrical, especially in 

 those birds which run. The tibia or leg-bone is long, and the fibula is present as 

 a small fine bone which usually coalesces with the tibia. 



The tarsus and metatarsus are represented by a single bone, which is very 

 various in length and shape in the different families of birds, and is one of the 

 most important members in classifying. 



The toes vary from five to two, but there are usually foxir : three anterior 



and one posterior. The number of bones in the toes (unlike mammals) vary 



according to the position of the toe, the outermost toe having five bones, and 



the innermost one bone, and the three intermediate toes having four, three, and 



. two bones respectively. 



Passing on to notice the breast-bone or sternum, we find it assume vei-y 

 much the shape of a boat, being convex outwards and of large size, and along 

 its median line is situated a projecting ridge called the keel, which ridge is 

 immensely developed in birds of powerfid flight, but nearly absent in cursorial 

 birds, such as the ostrich. The breast bone extends beyond the thoracic cavity 

 and embraces part of the abdominal also. 



The ribs of birds present great peculiarities, for there are, as it were, two 

 sets of ribs, one a vertebral and the other a sternal set ; these sets of ribs both 

 start in a posterior direction and join at an acute angle, and from the vertebral 

 ribs, which are the longest and strongest, a bony appendage proceeds upwards 

 and backwards and overlaps the next rib behind, the whole apparatus of vertebrae, 



K. ribs, and sternum forming an elastic, though fii-mly knit, case for the internal 



^■^ viscera. 



It should be mentioned that some of the ribs, both anterior and posterior. 

 are not attached to the sternum. 



The anterior members of birds, that is, the wings, are composed of bones 

 which are homologous to the bones in the arm of man ; they are the humerus 

 or the arm, the radius and ulna or fore-arm, the wrist or carpus, formed of two 

 small bones ; the metacarpus, of two tubular bones which have coalesced, and 



