SKELETON OF THE PIGEON. 509 



which reaches the sternum is called the sternal rib, and is 

 joined at an angle to the dorsal part of the rib, which articu- 

 lates with a vertebra. On the posterior surface of each of 

 the first four ribs there is an uncinate process. 



The skull has a rounded cranial cavity and a narrow 

 beak, which is mostly composed of the premaxillse. All the 

 bones are fixed except the quadrate, lower jaw, columella, 

 and hyoid. The surface is polished, the sutures are obli- 

 terated very early in life. 



The back part of the skull is formed by the basi-occipital, 

 the two ex-occipitals, and the supra-occipital. These bound 

 the foramen magnum through which the spinal cord passes 

 downwards from the brain. The basi-occipital forms most 

 of the single condyle on which the skull rotates. 



The top of the skull is formed from the paired parietals, 

 frontals, and nasals, the last being small, and in part super- 

 seded by the upward extension of the premaxill». 



The line of the upper jaw consists of premaxilla, small 

 maxilla, jugal, and quadrato-jugal, the last abutting on the 

 movable quadrate. 



Of the membrane-bones on the side of the skull, the 

 lachrymal in front of the orbit, and the squamosal above the 

 quadrate, are the most important. 



On the roof of the mouth we find that the basisphenoid, 

 which lies just in front of the basi-occipital, is covered over 

 by a membrane bone — the basi-temporal. In front of this 

 is a sharp " basisphenoidal rostrum," or parasphenoid, also a 

 membrane-bone. Articulating with the quadrate and with 

 the rostrum are the pterygoids, in front of these lie the pala- 

 tines, between which a part of the vomer may be seen. 

 The bony front of the palate is formed from inward exten- 

 sions of the premaxillae and maxillae. The inter-orbital 

 septum is formed chiefly from the mesethmoid but also from 

 the presphenoid. From the tympanum to the inner ear 

 extends the rod-like columella. The lower jaw originally 

 consists of numerous bones. The hyoid consists of a flat 

 " body," with anterior and posterior " horns." 



The pectoral girdle consists of sabre-like scapulse extend- 

 ing dorsally over the ribs, of stout coracoids sloping ven- 

 trally and articulating with the sternum, of the clavicles which 

 are united by the interclavicle to form the merry-thought. 



