NECTURUS MACULATUS. 395 
with the longitudinal axis of the vertebra. From there as far as §, it is gradually smaller 
and more depressed. After 8 it becomes again larger and more erect, so that the spine of 
21 is about equal to that of 5, and that of 22 surpasses it. It rapidly lengthens as far as 
26 to 27, where it reaches its maximum of length and is about equal to the haemal spine; 
from then on, both neural and haemal spines become gradually reduced as the vertebrae 
diminish in size. 
A haemal spine appears suddenly on the 22d to 24th vertebra, usually the 25d, an 
indication of it sometimes being found upon the previous vertebra in the form of a thin 
bony bridge which stretches across the ventral face of the vertebra from the outer angle 
of the transverse process to the centrum, thus covering the posterior portion of the ven- 
tral lamina. In one case noted, the vertebra just anterior to H bore upon one side a 
slender process, 4 to 5 mm. long, evidently representing an incomplete haemal arch. 
The first haemal spine is of about the maximum size, and, after three or four vertebrae 
in which this size is maintained, the haemal spines begin to diminish with the gradual 
reduction of the vertebrae, as in the case of the neural spines. The neural and haemal 
spines of the same vertebrae closely resemble one another, but, in the first few vertebrae 
that possess both, the former take a slightly more erect position while the latter ie more 
nearly parallel to the axis of the vertebrae. Towards the end of the tail both neural and 
haemal spines sometimes appear bifurcated at the tip, or even double as far as their base. 
In a given vertebra this may affect either spine alone or both spines. 
Zygapophyses. — In 1, the anterior zygapophyses are wanting and the posterior are 
near together. From 2 to S both sets are divergent and almost identical, save that the 
entire vertebrae at about 15 to 17 are a little wider than elsewhere and hence the 
zygapophyses are here farther apart. After 8 the vertebrae rapidly become narrow, and, 
beginning with H, both sets approach very near together and are reduced in size. They 
become obsolete at about 26, beyond which the vertebrae articulate solely by means of 
the vertebral centra. 
Ventral foramina.—These do not appear in the three anterior vertebrae and are 
usually of small size in 4. From then on, as far as H, there is usually a pair in each 
vertebra, although occasionally the foramen of one side may be converted into a notch 
by a deficiency in the ventral lamina. In H, where the roots of the haemal spine form 
thin laminae lying over the region of these foramina, openings occur not only in the ven- 
tral laminae as usual, but also in the laminae connected with the haemal spine, and the 
two sets of foramina are accurately superimposed. Beyond H the reduction of the entire 
transverse process renders the ventral foramina unnecessary, but in the two or three 
vertebrae succeeding H the new foramina through the base of the haemal spine may be 
present, although usually appearing upon but one side. 
