1870.] AXIAL SKELETON OF THE URODELA. 263 
category of paraxial parts. Were they really hzemal arches (7. e. re- 
presentatives of the membranous connexions between the distal ends 
of the two series of ribs), we should have to adopt the somewhat 
violent conception that the lower parts of the hzemal arches of the 
tail are detached from their proximal portions, and fixed directly to 
the under surface of each supporting centrum. For if the caudal 
vertebree from before backwards are examined, it will be seen that 
the first hypapophysial arch is not formed by the bending down of 
the transverse processes, or by an extension of ossification along the 
membrane, connecting the distal ends of such transverse processes, 
but that it arises suddenly beneath the centrum. This is well shown 
in the sixty-fourth vertebra of Amphiume (fig. 1). In this vertebra 


Under view of last trunk- and anterior caudal vertebrae of Amphiwma (No. 579 4 
in College of Surgeons’ Museum*). 
Hy. Hypapophysis. 
the caudal hypapophysis first makes its appearance as a long process 
on each side, the two processes being medianly disunited below, and 
distinct from the transverse process, which exists as completely in 
this vertebra as in the one preceding it. 
The three systems of parts, epaxial, paraxial, and hypaxial, are 
variously united together respectively. 
The epaxial parts, or neural arches, are serially connected together 
by means of special articular processes, eygapophyses. Lach ver- 
tebra is provided with two of these in front and two behind, the 
posterior pair of which have their articular surfaces directed down- 
wards, and somewhat obliquely outwards (fig. 16), reposing on the 
upturned and somewhat inwardly directed surfaces of the anterior 
zygapophyses of the vertebra next behind. The cervical vertebra 
forms an exception, inasmuch (fig. 19) as it has no anterior zyga- 
pophyses, but has special modifications for articulation with the 
skull. 
The paraxial parts are never serially connected together, but by 
muscular or connective tissue, except the occasional coalescence of 
such parts in the sacral region. 
The hypaxial parts in the tail form with each other serial con- 
nexions more or less simulating those existing between the successive 
neural arches. 
* The figures of specimens in the Museum of the College of Surgeons have 
been drawn by the kind permission of the authorities of that institution. 
