EMERSON: ANATOMY OF TYPHLOMOLGE. 
53 
The caudal vertebrae. — These are shorter, more compressed, and 
without transverse processes, so that the lateral plate of the neural 
arch is increased at the expense of the dorsal one. The transition 
takes place rapidly in the first three caudal vertebrae, the fourth 
being typical of the modified form. The neural spine becomes very 
prominent in the third and continues with little change, disappearing 
at the 24tli or 25th. 
The postzygapophyses approach one another and become articular 
surfaces on the ventral surface of the neural spine. The pre- 
zygapophyses also approach each other and are contiguous. 
On the fourth caudal vertebra appears the haemal arch, which is 
typical of the caudal vertebrae in general. It appears suddenly and 
is formed by two ventral processes from the lateral portions of the 
centrum uniting distally, thus forming a ventral arch through which 
the caudal artery passes. This is similar to the neural arch, but 
somewhat smaller and bears a small rounded haemal spine, projecting 
postero-ventrally. 
This compressed form with a dorsal and a neural arch is found 
almost unchanged, save for a gradual diminution in size, from the 
fourth to the 24th or 25th caudal vertebra. Posterior to these, the 
vertebrae decrease rapidly in size and the neural and haemal spines 
disappear, the neural arch persisting to the 32d, the haemal arch to 
the 33d caudal vertebra. The 34th and 35th vertebrae are tiny 
centra, cylindrical rather than of the hour-glass shape. 
The ribs. — The ribs which are borne on the second to the sixteenth 
vertebra inclusive, differ little in size and form. Each consists of two 
heads, one dorsal or tubercular and the other ventral or capitular, 
which articulate with the transverse process of the vertebra and unite 
to form a shaft. This is slightly longer than the heads and is pro¬ 
longed distally by a short cartilaginous rod. The rib is flattened 
antero-posteriorly, the posterior surface being slightly concave. 
Its general direction is postero-ventral, continuing that of the trans¬ 
verse process. The sacral rib articulates distally with the dorsal end 
of the ilium, and has no cartilaginous prolongation, but is slightly 
heavier than the other ribs. 
The most important difference in the vertebral column between 
Typhlomolge and the Proteidae is in the first vertebra. The three 
long anterior processes by which it articulates with the skull are not 
found in Necturus or Proteus but they are duplicated in the larval 
Spelerpes ruber (W. K. Parker, ’ 82 , pi. 20, figs. 1 and 2). 
