62 PROF. W. K, PAEKER ON THE 



condition seen in the free caudal series. The first of that series (PI. IX. fig. 4, cd.v}, 

 ic.) sends an intercentrum under the fourteenth or last sacral ; the rest up to the foi'e- 

 part of the uropygial tract have increasingly lai-ge intercentra traced from before 

 backwards; in the Common Fowl these parts are suppressed. Above (PI. VII. & 

 Pi. IX. fig. 5) the neural arches are seen to be narrow, and the spines low and blunt, 

 in these free vertebrae. The short uropygial series of four imperfect segments formed 

 on the end of the notochord is pinched in between the third and fourth, and the last 

 segment expands a little. The ossification of the sacral series, as seen in the 3rd stage, 

 is by a pair of centres for each arch and one for each centrum (PI. IX. fig. 6) ; there 

 is in many young birds the appearance of a double bony centre in this part ; it is 

 really single, the osseous matter which is first formed round the notochord growing 

 out as a right and left lobe into the surrounding cartilage. The ossification of the 

 caudal series is like that of the uro-sacrals in front, but becomes simpler behind ; the 

 intercentra are separately ossified. The vertebral chain of the adult may be profitably 

 compared with that of some other types ; in the following formulse the avian sacrum 

 is taken as one region : — 



CORYTHAIX BDFf'ONI, 



C. 14, the two last with free ribs; D. 5, all with arches perfect; S. 13, first witli 

 half-sized free ribs, altogether, four pairs of pre-iliac buttresses, and the rudiments of 

 a fifth, the ninth or first uro-sacral has riblets ; Cd. 7-f 3 : Total 42. 



Opisthocomus ceistatus. 



C. 19, last two with free ribs, sixteenth and seventeenth with no capitular develop- 

 ment of fused riblets ; D. 3 ; S. 15, of which five have pre-iliac buttresses, the first 

 two of these with free ribs, the second of whicli have sternal pieces incomplete below, 

 the tenth and eleventh or first and second uro-sacrals have riblets; Cd. 5 + 4: 

 Total 46. 



Chaujsta chavaria. 



C. 19, last three with free ribs; D. 5, ribs devoid of appendages ; S. 17, with eight 

 pairs of pre-iliac buttresses, the first three of these with developed ribs and sternal 

 pieces, the twelfth and thirteenth and probably the fourteenth had distinct riblets ; 

 Cd. 6 + 5: Total 52. 



Crax globicera. 



C, 16, two last with free ribs ; D. 4; S. 16, the first six with pre-iliac buttresses, of 

 these the first carries perfect ribs, then two follow with no lateral processes, the next 

 two have strong diapophyses and feeble riblets ; three sacrals follow with these parts 



