360 



ZOOLOGY 



SECT. 



bone, the pygostyle or ploughshare-bone (Fig. 968, pyg.st.) t formed 

 by the fusion of four or more of the hindmost caudal vertebrae. 



Thus the composition of the vertebral column of the Pigeon may 

 be expressed in a vertebral formula as follows : 



Syn-sacrum. 



Cerv. 14. Thor. 1+3 + 1. Lumb. 6. Sacr. 2. Gaud. 5 + 6 + 4 = 42. 



The sternum (Fig. 968, st.) is one of the most characteristic 

 parts of the Bird's skeleton. It is a broad plate of bone produced 



ventrally, in the sa- 

 gittal plane, into a 

 deep keel or carina 

 sterni (car.), formed, 

 in the young Bird, 

 from a separate cen- 

 tre of ossification. 

 The posterior border 

 of the sternum pre- 

 sents two pairs of 

 notches, covered, in 

 the recent state, by 

 ligament ; its anterior 

 edge bears a pair of 

 deep grooves for the 

 articulation of the 

 coracoids. 



The shall (Fig. 

 971) is distinguished 

 at once by its rounded 

 brain-case, immense 

 orbits, and long, 

 pointed beak. The 

 foramen magnum 

 (/. m.) looks down- 

 wards as well as 

 backwards, so as to 

 be visible in a ven- 

 tral view, and on its 

 anterior margin is a 

 single, small, round- 

 ed occipital condyle 

 (o.c.). Most of the 

 bones, both of the 

 cranial and facial regions, are firmly ankylosed in the adult, and 

 can be made out only in the young Bird. 



The occipitals, parietals, frontals, and alisphenoids have the usual 



an 



fir 



FIG. 971. Columba livia. Skull .of young specimen. A 

 dorsal; B, ventral; C, left side, al.s. alisphenoid; an. 

 angular ; ar. articular ; b. o. basi -occipital ; d. dentary ; e. o. 

 ex-occipital ; eu. aperture of Eustachian tube ; /. m. foramen 

 magnum ; ft: frontal ; i. o. s. inter-orbital septum ; ju. jugal ; 

 Ic. lacrymal ; Ib.s. lambdoidal suture ; m.eth. mesethmoid ; 

 mx. maxilla ; mx. p. maxillo-palatine process ; na. na'. na". 

 nasal ; o.c.' occipital condyle ; or. ft: orbital plate of frontal ; 

 wa. parietal ; pa.s. parasphenoid (rostrum) ; pi. palatine ; 

 p. mx. pre-maxilla; pt. pterygpid ; 511. quadrate; s. an. 

 supra-angular; s. o. supra-occipital; sq. squamosal ; ty.' 

 tympanic cavity ; II XII, foramina for cerebral nerves. 



Parker's Zootomy.) 



