243 



Describe (1) the Vertebral Column, and (2) the Skull of the 

 Pigeon. 



(1) The five regions are cervical or neck, thoracic, lumbar, 

 sacral, caudal. There are 14 heterocoelous cervical verte- 

 brae ; the first two (atlas and axis) are small and without 

 ribs, the next ten have each a pair of vestigial two-headed 

 ribs, the heads being fused to the centrum and transverse 

 process (each side) and enclosing spaces (vertebra-arterial 

 foramina) through which the vertebral arteries pass. The 

 ribs of the last two cervicals are less rudimentary, and are 

 not fused to the vertebrae. The first three thoracic verte- 

 brae are fused together ; the last one (the fifth) is fused 

 along with the five lumbars, the two sacrals and the first 

 five caudals to form the sacrum. The next six caudals 

 are free ; and the last four or five, adpressed and fused, 

 form the upturned pygostyle. 



There are five well-developed thoracic ribs. The upper 

 or vertebral portion of each rib has two heads (a capitulum 

 articulating with the centrum of the vertebra, a tubercle 

 articulating with a transverse process) and an uncinate 

 process, projecting backwards. The lower or sternal 

 portion articulates with the broad sternum, which has a 

 deep keel. 



(2) The cranium is flexibly connected with the (movable) 

 facial portion of the skull. The large orbits, almost in 

 front of the cranium, are separated by a thin vertical 

 interorbital septum only. 



The base of the cranium consists of the basitemporal 

 (covering part of the basisphenoid* ) and the basisphenoidal 

 rostrum.* The back of the cranium is formed by the 

 basioccipital* (bearing the single condyle for articulation 

 with the atlas), the two exoccipitals* and the supraoccipital* ; 

 and these surround the foramen magnum. Paired parietals 

 and frontals form the roof of the cranium ; and at its sides 

 are the tympanic cavities (recess with fenestra ovalis and 

 columella*) bounded above by the squamosals, each of 

 which has a projecting zygomatic process meeting a similar 

 process of the frontal that is descending and post-orbital. 

 (The jugal has no ascending process meeting the zygomatic, 

 the orbit is therefore confluent with the temporal fossa 

 behind.) At the front of each orbit there is a lachrymal. 

 The interorbital septum* is mainly mesethmoid* and 

 presphenoid.* 



The facial portion of the skull consists of the small 

 nasals, the long premaxillae (upper beak), and the bones 

 of the upper jaw and roof of the mouth. The upper jaw 



