220 PEOF. W. K. PAEKEE ON THE 



dorsals. I find no intercentra in the caudal region, either in embryo, young, or adults, 

 beyond a pair of thickenings under the 1st and 2nd of the imperfect uropygial segments. 



VI. — Sacral Vertebra of a recently hatched Quail (Coturnix communis), answering 



to the 6th stage of the Chick. 



Leaving out two stages, I come to the 6th, and in this case, for the sake of comparison 

 with the Hemipod (Plate XXV. fig. 5), I have figured the sacrum of the newly hatched 

 Quail (Plate XXV. fig. 4), instead of that of its large relative. The difference between this 

 sacrum and that of the Common Fowl is, that I can in the former only find one pair of 

 uro-sacral riblets ; the last uro-sacral of the Powl corresponds with the first caudal of the 

 Quail ; the number of vertebrae is the same in both. The ossification of the neural 

 arches is only imperfectly seen in this lower view, but these osseous centres are to be seen 

 running into the diapophyses in the hinder half of the sacrum. This part is sufficient 

 to illustrate what takes place in the pre-sacral part of the chain ; the 1st uro-sacral shows 

 how the remnants of ribs are ossified, the small bony tract soon loses its independence. 

 In the 2nd to the 4th — the lumbo-sacral series — the originally separate riblets have be- 

 come fused with the thick diapophyses that buttress the pre-ilium ; they may have a 

 distinct osseous centre, but I do not find it in these Gallinaceous birds. The spindle-shaped 

 series of centra look, especially in the middle region, as though there were two bony 

 centres in each centrum; this, however, is not the case, the bony matter is just deposited 

 around the notochord, in its sheath, and then affects the cartilaginous mass right and 

 left, in two wings as it were. The distinction of bony centres is gradually lost in the uro- 

 pygial series. 



VII. — The Vertebral Chain in the last stage, or Adult Fowl. 



Notwithstanding the somewhat lowly position of this type, it has, in common with the 

 much more lowly struthious birds, a vertebral chain of a very high type ; this is not to 

 be wondered at when we see the same thing in that extinct toothed bird, Marsh's Hes- 

 peromis, an archaic " pygopod " in which one would have expected to find vertebras at 

 least as Reptilian as those of the existing Penguins. This should be borne in mind by 

 those Ontologists who desire to derive all these birds from an Arch&opteryx ; an hypo- 

 thesis this, which to me appears to be very hard and difficult and unlikely, for I can- 

 not imagine all the Cretaceous, Tertiary, and modern birds as potentially lying in the 

 loins of that ungainly kind of feathered Powl. 



The vertebral formula of the adult differs from that of the embryo ; for the sternal 

 piece of the 16th vertebra becomes absorbed, making that joint the last of the cervicals, 

 and the last five joints of the chain become soldered into one, the " ploughshare " or uro- 

 pygial bone. The various regions — cervical, dorsal, dorso-sacral, lumbo-sacral, sacral 

 proper, uro-sacral, and caudal — may be put as follows : — 



C. 16, two ribs free and last joint ankylosed to the next region ; D. 4, the 4th only 

 free ; D.-S. 1 ; L.-S. 3 ; S. 4 ; U.-S. 7, the 1st with a riblet ; Cd. 10+4, the last five being 



