sdcrurri (cf. Reptiles] consists of a fusion of one or more 

 thoracic vertebrae with the lumbars, sacrals and some 

 caudals. The last few caudals fuse to form the pygostyle 

 or ploughshare bone of the short tail. The shoulder girdle 

 has stout coracoids articulated with the sternum, sabre - 

 shaped scapulae (overlying the ribs, which have uncinate 

 processes), and a V-shaped " merrythought " (clavicles 

 united with an interclavicle). The sternum is broad, and 

 has (except in Ratitae} a ventral keel to which the big 

 pectoral muscles are attached. Generally the fore-limb 

 has only three digits ; and the distal carpals are fused with 

 the metacarpals, forming a carpo-metacarpus. The ilia 

 of the pelvis are ankylosed with the sacrum ; the slender 

 ventral pubes and the broad ischia (between ilia and pubes) 

 are directed backwards, and neither are united ventrally, 

 except in Struthio, the African Ostrich (pubic symphysis), 

 and in Rkea, the South American Ostrich (ischial symphysis). 

 The proximal tarsals are fused with the tibia (tibio-tarsus), 

 and the distal tarsals with metatarsals 2, 3 and 4 (tarso- 

 metatarsus); therefore the ankle-joint is intertarsal. The 

 first metatarsal is free ; the foot has four digits or toes 

 (with claws). 



The large cerebral hemispheres overlie the thalamence- 

 phalon and the optic lobes (displaced to the sides), and meet 

 the cerebellum. The olfactory lobes are small, and the 

 nasal organ is weakly developed ; the nostrils are situated 

 at the base of the beak, the internal nares are between the 

 palatine and vomers. The eye has a large pecten, a nicti- 

 tating membrane, and sclerotic ossicles. The ear has a 

 long and curved lagena (auditory organ) ; there is only one 

 ossicle, the columella. There are twelve pairs of cranial 

 nerves. 



The solid spongy lungs, fixed against the ribs, are only 

 slightly expansible. Connected with the lungs there are 

 large air-sacs throughout the body, and these communicate 

 with the pneumatic cavities in the bones. Expiration is 

 the more active breathing process. The trachea is supported 

 by bony rings; its upper portion, the larynx, is without 

 vocal cords ; its terminal portion, where it divides into the 

 bronchi, forms the syrinx, which is the vocal organ. The 

 heart has four chambers, the auricle and ventricle of the 

 right side are completely separated from those of the left ; 

 the right auriculo-ventricular valve is muscular. Only the 

 right aortic arch is present in the adult. The renal portal 

 system is practically absent. The kidneys (metanephros) 

 are three-lobed ; the urine is semi-solid. The ureters and 

 genital ducts, and the gut, open into a common cloaca. 



R 



