GENERAL CHARACTERS OF BIRDS 



727 



the basisphenoid. There is an interorhital septum formed 

 from presphenoid and mesethmoid. The otic bones fuse with 

 adjacent bones and with one another about the same time. 

 In modern birds there are no teeth ^ but the jaws are covered 



Qk S.I 



Fig. 428. — Position of organs in a bird, diagrammatic. 

 — After Selenka. 



C, Cere around the nostril ; E., ear-opening ; GU., gullet ; TR., trachea ; CR., 

 crop ; PV., proventriculus ; H., heart ; LV., liver ; KE., keel of sternum ; 

 GI., gizzard ; S.I., small intestine ; CA., one>of the two intestinal caeca ; L.I., 

 large intestine ; CL., cloaca ; P., pygostyle ; UR., ureter ; KI., kidney, em- 

 bedded in the ilia ; A.S., a posterior air-sac ; LU., lung attached to the ribs ; 

 CB., cerebellum ; O.L., optic lobe, thrust to the side ; C.H., cerebral hemisphere. 



by horny sheaths. The premaxillce are large, and form most 

 of the beak. There is a complete infra-temporal arcade 

 formed by a delicate jugal and quadrato-jugal reaching back 

 to the quadrate. The supra-temporal arcade is usually 

 incomplete, but in some cases a process of the squamosal joins 



