238 
ORIGINAL ARTICLES. 
separate and serve to inclose a caudal artery and vein. They 
correspond in position and form to the similarly named parts in 
fish, the transverse processes in question being new parts, which are 
wanting in Fish. Furthermore, the ribs of the higher vertebrata 
do not correspond with the ribs of Fishes, which are seen to pass 
gradually into their inferior caudal arches, but are, as Johannes Muller 
has conclusively demonstrated (Yergl. Anat. der Myxinoiden Theil. 
1. p. 93—100.) parts of a peculiar nature, absent in Fish and 
arising higher up on the vertebral centra than the ribs of these 
last animals. 
§ 4. The rings, developed from the investing mass of the 
notochord, which have been described, gradually thicken and 
broaden on all sides, become filled up by a mass similar to that 
of which they originally consisted, and change into vertebral 
centra ; the notochord, becoming more and more constricted where 
it is inclosed by them and at length disappearing. In Amphibia, 
Birds and Mammalia it, at length, entirely disappears, but this is 
not the case in all osseous fish. In all these animals, however, a 
part of it remains between every pair of rings or vertebral bodies. 
The sheath of this part becomes an intervertebral ligament, while 
the axial portion is liquefied, and then appears as a more or less 
viscid synovial fluid, or, as in Mammals, may be entirely absorbed. 
§ 5. Each vertebral body, together with its different processes, 
though at first entirely consisting of granular blastema—gradually 
becomes cartilaginous and, even in this condition, it occasionally 
happens that all its parts form one continuous whole. But if a 
process becomes distinct, as a rib, the mass becomes membranous at 
the point of demarcation. 
The rest of the investing mass of the notochord which has remained 
between the vertebral centra, almost always becomes membranous, 
(very rarely, as in the most anterior part of the spinal column of 
the Sturgeon, also cartilaginous), covers the intervertebral ligaments, 
and then appears continuous with the periosteum of the vertebral 
body. The same process appears to take place in those parts which 
lie between successive spines and neural arches, the intercrural and 
interspinous ligaments appearing to be developed here. 
§ 6. It results from existing observations that the ossification of 
the vertebral bodies begins at different points and proceeds in different 
modes. In each crus of a neural arch, however, only a single centre of 
ossification is developed, which gradually elongates, so that, at length, 
the entire crus appears ossified, whereupon it anchyloses with the bony 
deposit in its centrum. In each rib also, ordinarily, only one centre 
of ossification is developed, and this extends in such a manner, that 
in many animals, the entire rib ossifies, while, in others, only the 
greater part of it is converted into bone, the lesser moiety remaining 
cartilaginous, and forming what is termed the costal cartilage. In 
Birds, on the contrary, two ossific centres appear in almost every rib, 
one for the upper half, the other for the lower half; the latter cor- 
