GENERAL CHARACTERS OF BIRDS. 651 
there are only two separate carpals, the others fusing with the 
metacarpals, and thus forming a carpo-metacarpus. The 
thumb ts often clawed, the second digit rarely. 
The ilia of the pelvis may be firmly fused to the complex 
sacrum ; the acetabulum is incompletely ossified; the pubes 
are directed backwards parallel to the tschia. There is no 
pubic symphysis except in the African ostrich (Struthio), and 
no ischiac symphysis except in the American ostrich (Rhea). 
in the hind-limb the fibula ts incomplete, and more or less 
united to the tibia, the proximal tarsal bones are united to 
the distal end of the tibia (which ts 
therefore calied a tibio-tarsus), the others 
being united to the proximal end of three 
united metatarsals (which thus form a 
tarso-metatarsus). As in Reptiles, the 
ankle-joint ts therefore intertarsal. The 
maximum number of toes is four, of 
which the first ts the hallux: if there be 
four, the metatarsal of the hallux ts free 
from the other three fused metatarsals ; 
uf there are only three, the hallux has been Fre: 946) —Disgrim- 
suppressed. . matic section of 
In regard to the alimentary system, the young bird.—After 
absence of teeth, the frequent occurrence of Gadow. 
a crop and a gizzard, the usual shortness n., Spinal cord, v., ver- 
of the large intestine, the presence of a ect Mgt irean, 
spl 
liver; G., gut; som. 
cloaca, may be noted. (ottea ate be 
The heart is four-chambered ; the single (dotted), splanchnic 
aortic arch curves to the right side; only [ay Oh, mespvlasts 
the pulmonary artery rises from the right productive organ; K., 
ventricle ; the two valves between the right 
auricle and the right ventricle are in part muscular , there ts 
no renal portal system , the red blood corpuscles are oval and 
nucleated ; the blood temperature is from 2°-14° F. higher 
than that of Mammals. 
The non-expansible lungs are fixed to the dorsal wall of 
the thorax , the bronchial tubes expand in irregular branches 
in the lungs ; the ends of some of these branches are continued 
into surrounding air-sacs ; these may be continued into the 
bones, and end in minute air-spaces. The trachea has bony 
rings, a larynx (without vocal chords) at its upper end, and a 
