COLUMBA. 371 
five thoracic vertebree bear ribs which articulate distally with 
the sternum. Each rib has a longer vertebral part and a 
shorter external part, and the former has two heads arti- 
culating with its vertebra. The first four have short 
uncinate processes. The capitulum of the rib articulates 
with the centrum of the vertebra and the suderculum with 
the transverse process. The first three thoracic vertebree 
are fused, the fourth is free, while the fifth is involved in 
the sacrum. 
In the young bird there are five free lumbar vertebra 
and then ¢wo sacral to which the ilium is attached, but as 
development proceeds the ilium grows forwards and becomes 
attached to all the lumbar and to the fifth thoracic. Simi- 
larly there are in the young bird fifteen free caudal vertebree, 
and the ilium gradually grows backwards and fuses with five 
of these. Of the other ten the last four fuse together to 
form the pygostyle. 
This means that the young bird presents us with a 
reptilian-like condition of the vertebral column in which 
all the vertebrz are free. They consist of— 
Ceivicall jchecndsean decane suatis 14 
TPROTACIC 2 x..g2ec0s ehsieose ane 5 
Lia bak 2.4.4 ncodacsiendsensions on 5 
Sacral: gaianccanrenebsou star 2 
Catal. aed Soaked deseo. 15 
The modifications then take place as age advances. 
1. The first three thoracic become ankylosed or fused. 
2. The last four caudal become ankylosed to form the 
pygostyle. 3. The ilium grows forwards and fuses with all 
the lumbar and the last thoracic, and backwards to include 
five caudals. 
Cervical. Thoracic. Lumbar. Sacral. Caudal. 
14 [3] #rtr1+5+24+5+6+ [4] 
ta por 
These fusions are supposed to be a recapitulation of 
similar modifications which have taken place gradually in 
the descent of birds from reptiles and in adaptation to the 
gradual adoption of flight and bipedal progression. It will 
be remembered that a similar fusion of vertebrae into an 
anterior vertebral plate is found in the skate, in which the 
