xm 



PlIVLr^r THORDATA 



387 



cartilage as in Reptiles, and articulates with the vertebral rib by a 

 synovial joint. Springing from the posterior edge of the vertebral 

 rib is an v.nrinate (unc), resembling tliat of Sphenodon and the 

 Crocodile, but formed of bone and ankylosed with the rib. 



Following upon the fourth or fifth thoracic are about twelve 

 vertebne all fused into a single mass (Fig. 1027, s.scr.), and giving 

 attachment laterally to the immense pelvic girdle. The whole of 

 this group of vertebne has, therefore, the function of a sacrum, 

 diflfering from that of a Reptile in the large number of vertebne 

 composing it. The first of them bears a pair of free ribs, and is, 

 therefore, the fifth or sixth (last) thoracic 

 (fh.v.o). The next five or six have no 

 free ribs, and may be looked upon as 

 lumbar (Fig. 1029, /. 1—s. 3) : their trans- 

 verse processes arise high up on the neural 

 arch, and the ligament uniting them is 

 ossified, so that the lumbar region -pve- 

 sents dorsally a continuous plate of bone. 

 Next come two sacral vertebrae (c.l) 

 bomolosfous with those of the Lizard : 

 besides transverse processes springing 

 from the neural arch, one or both of 

 them bears a second or ventral outgrowth 

 (c.r.) springing from each side of the 

 centrum and abutting against the ilium 

 just internal to the acetabulum. These 

 distinctive processes are ossified inde- 

 pendently and represent sacral ribs. The 

 five vertebne of the pelvic 

 are caudal. Thus the mass of 

 ^'ertebKe supporting the pelvic girdle 

 in the Pigeon is a compound sacrum, or 



remaniing 



region 



Fig. 1029.— Columba livia. 



Sacrum of a ixcstliiig (abmit 

 fourteen daj-s old), ventral 

 aspect. (-1. centrum of first 

 sacral vertebra ; ci. 'centrum of 

 fifth caudal ; c. r. first sacral 

 rib; /I. centrum of first lumbar ; 

 ?•'. of third lumbar ; 6-1, of fourth 

 r» lumbar; s^, of sixth lumbar; 

 tr. 'p. transverse process of first 

 lumbar; tr.'p'. of fifth lumbar ; 

 tr. p.". of first sacral. (From 

 Parker's Zootomy.) 



fusion of the 



lumbar and sacral, and the anterior 



syn-sacrum, formed by the 

 posterior thoracic, all the 

 caudal vertebrae. 



The syn-sacrum is followed by six free caudals, and the vertebral 

 column ends posteriorly in an upturned, compressed bone, the 

 fygostyh or ploughshare-bone (Fig. 10^^. pyg. si.), formed by the 

 fusion of four or more of the hindmost caudal vetebrte. 



Thus the composition of the vertebral column of the Pigeon may 

 be expressed in a vertebral formula as follows: — 



Syn-sacnxni. 



Pyg- 



Cerv. 14. Tlior. 4oro-rl. Lumb. 5 or 6. Sacr. 2. Caiid. 5 + + 4 =:43. 



T\ie sternum (Fig. 1027, s^.) is one of the most characteristic 

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



