596 BIRDS. 



In the hind-limb the fibula is incomplete, and more or less 

 united to the tibia ; the proximal tarsal bones are united to 

 the distal end of the tibia (which is therefore called 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 is therefore intertarsal. The 

 maximum number of toes is four, of which the first is the 

 hallux ; and if there be four, the metatarsal 

 of the hallux is free from the other three 

 fused metatarsals. 



In regard to the alimentary system, the 

 absence of teeth, the frequent occurrence of 

 a crop and a gizzard, the usual shortness 

 of the large intestine, the presence of a 

 cloaca, may be noted. 



The heart is four-chambered ; the single 

 ^pT aortic arch curves to the right side ; only 



m __. the pulmonary artery rises from the right 



niatic section of ventricle ; the two valves between the right 

 young bird.— After auricle and the right ventricle are in part 

 Gadow. muscular; the red blood corpuscles are 



"'UbraT' r° rd rib •' T.', oval and nucleated ; the blood temperature 

 liver; p., gut; som. i s from 2°-ia° F. higher than that of 



(dotted), somatic layer -.. - 7 J 



of mesobiast; spt. Mammals. 



ia°er ed of mesobiast^ ^ ne non-expansible lungs are fixed to 



ao., aorta; r., re- the dorsal wall of the thorax; the bron- 



Productive organ ;K., ^ /fl/ ^^ gx p and in i rregu l ar b ranc hes 



in the lungs ; the ends of some of these 

 branches are continued into surrounding air-sacs ; these may 

 be continued i?ito the bones, and end in minute air-spaces. 

 The trachea has bony rings, a voiceless larynx at its upper 

 end, and a syrinx or song-box {with vocal cords) at the 

 origin of the bronchi. Expiration is the more active part of 

 the respiratory process. 



The (metanephric) kidneys are three-lobed, and lie em- 

 bedded in the pelvis ; the ureters open into the cloaca ; there is 

 no bladder; the urine is semi-solid, and consists chiefly of urates. 



The testes lie beside the kidneys ; the vasa deferentia run 

 outside the ureters, and open into the middle region of the 

 cloaca. The right ovary atrophies, the right oviduct is rudi- 

 mentary. 



