1887.] 



On the Morphology of Birds. 



53 



Amongst the Carinatae, which lie in the intermediate space, there 

 is none better for the purposes of study than the common fowl ; to 

 this type I have devoted most attention, and have now worked oat 

 the limbs in as many stages as I formerly did the skull. 



I can now give an account of the vertebral column with the ribs and 

 sternum, the limb-girdles and limbs, from the end of the seventh day 

 of incubation ; by which time the hyaline cartilage is perfect, and 

 certain even of the bony tracts are begun. 



The fowl is an intermediate form between the emeu and the pigeon ; 

 but most akin to the latter. I shall now confine myself to what is 

 seen in the development of the skeleton (excluding the skull) in this 

 medium type. 



The vertebral column, at the end of a week's incubation, is formed 

 of hyaline cartilage ; up to the end of the true sacrals, the notochord 

 is completely invested with cartilage ; but, behind those four segments, 

 only at the sides. 



The notochord has its constrictions in the middle of each centrum, 

 and is most dilated at the intercentra. 



The neural arches do not nearly meet above ; the atlas is in four 

 pieces — a superficial and an inner piece to the centrum, and a pair of 

 arch-rudiments ; the inner segment of the centrum becomes the 

 odontoid process of the axis. 



Between the axis and the first true sacral, all the vertebras have 

 separate ribs ; in the cervical region, except near the dorsal region, 

 there are small styloid cartilages lying horizontally, which have their 

 head, or thick end, wedged in between the upper and lower transverse 

 processes. Near the dorsals they are transversely placed, and then 

 begin to develop a descending process. 



The first vertebra of this stage with complete ribs becomes, by 

 absorption of the lower part of the arch, the last cervical in the 

 adult. Behind the twenty pre-sacrals there are fifteen sacrals, and 

 this series has its subdivisions. 



The first develops ribs (it is dorso-sacral), the next three develop 

 minute but distinct ribs, like those near the lower part of the neck ; 

 these are lumbo-sacral. Then come the four sacrals with no ribs, and 

 then the seven uro-sacrals, the first two of which have rib-bars that 

 ossify separately, below the upper transverse processes, which latter 

 form a complete series from the third cervical to the last free caudal 

 segment. 



Of those there are five ; then come five more paired imperfect rudi- 

 ments, clinging to the terminal part of the notochord. 



At the end of the 8th day there are six of these, with the last elon- 

 gated, and the notochord projecting behind far enough for three or 

 four more rudiments. 



At the end of the 10th day the vertebral chain has undergone a great 



