402 



THE PIGEON. PHYLUM CHORDATA 



share bone or pygostyle, which consists of four fused vertebrae 

 and supports the tail. Each rib has a head or capitulum which 

 articulates with the centrum of its vertebra and a tubercle 

 which articulates with the transverse process. Those which join 

 the sternum are bent forwards at an angle to do so, the part 

 above the angle being known as the vertebral rib, that below 

 as the sternal rib. Both parts are bony in the pigeon, whereas 

 in the rabbit the sternal ribs are cartilaginous. On the hinder 

 side of each of the free ribs, except those of the last pair, is an 

 uncinate process. 



THE SKULL 



The skull (Figs. 316, 317) has very large orbits, which are 

 situated almost entirely in front of the cranium, so that the eyes 

 are separated not by the whole width of the brain, but merely 



i.o.s. I. 



e. oc. 



Fig. 316. — The skull and some of the cervical vertebrae of a pigeon, from the 



left side. 



d., Dentary ; Eu., Eustachian tube ; e.oc, exoccipital ;/.f., fenestra! recess ;/r., frontal ; i.o.s., interorbital 

 septum ; lac., lacrimal ; n., nasal ; par., parietal ; pi., palatine ; ptn., premaxilla ; p.o.p., postorbital 

 process of frontal ; pt., pterygoid ; g., quadrate ; s.o.b., suborbital bar ; s.oc, supraoccipital ; sa., supra- 

 angular ; sq., squamosal ; zy., zygomatic process of the squamosal ; /., //., foramina for first two 

 cranial nerves ; 1-3, first three cervical vertebrae. 



by an interorbital septum. In the adult, separate bones can 

 hardly be distinguished in the skull, and the following account 

 is based on what can be seen in the embryo and young bird, 

 particularly in the domestic fowl. 



The foramen magnum is surrounded by basioccipital, supra- 

 occipital, and two exoccipitals, and there is a single condyle 



