NECTURUS MACULATUS. 
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one, the pleurapophysis, is associated 
with the centrum. The investing bony sat Pees ce niet 
: . i Neurapep 
mass is formed secondarily about these Pest 2ygobebhs 
Diaper 
rods by periostosis and consists essen- 
_7 Dorsal Laces 
tially of two simple investing sheaths 
SacweF For 
Cartilage 
and two flattened laminae, of which Lateral Coming — 
of Neural arch 
one is vertical and dorsal, connecting 
the two sheaths, and the other horizon- peatey. 
Fossa. Post Comcevily 
of Centrum 
tal and ventral, applied to the ventral 
side of the pleurapophysial sheath and Fig. 4. 16th vertebra; posterior end view. X83. 
spreading out proximally over nearly 
the entire length of the centrum, with which it becomes fused. This latter lamina is 
perforated by the ventral foramen, situated immediately posterior to the pleurapophysis 
and transmitting the collateral vertebral vessels. As the dorsal lamina meets the ventral 
one nearly at right angles, they form with the side of the centrum, two fossae, the anterior 
and the posterior vertebral fossae. The posterior fossa is much the deeper and communi- 
cates with the region ventral to the vertebral column by means of the ventral foramen 
just mentioned. 
In the larva the cartilaginous diapophysis and pleurapophysis are directly contin- 
uous proximally with a lateral mass, the “rib bearer” (Rippentriiger) of Gippert, while 
distally they unite to form the cartilaginous rib, the whole mass being at this time a con- 
tinuous piece. The process of ossification within and around the rib bearer and the sides 
of the vertebrae, and especially the growth of the osseous sheaths about these rods, gradu- 
ally cut them off from one another and restrict them proximally into tapering points, so 
that in a macerated adult vertebra, from which all the cartilage has been removed, the 
moulds of the parts in question are seen as very deep and conical pockets. 
Later ossification separates the free rib from the encasing sheaths of the transverse 
process, and joints are thus formed between the two bodies. The part of the rib thus 
segmented from the diapo hysis forms the tubercular process and the part once in con- 
nection with the pleurapophysis becomes the capitular process, both processes retaining 
throughout life an articular connection with the rods from which they originally separated. 
Embryological investigation has rendered it probable that the pleurapophysis and 
its associated capitular head represent the primary condition, and that the cartilage of the 
rib bearer becomes dorsally extended for increase of support, developing later the second- 
ary or tubercular attachment. Géppert has shown this secondary growth of the tuber- 
cular connection in the case of Triton and some other Urodeles, a growth which proceeds 
from the ribs and follows along a line of connective tissue until it reaches the rib bearer 
