1870.] AXIAL SKELETON OF THE URODELA. 279 
caudal is in the same case; but at the third, or sometimes the second 
caudal, this process suddenly reappears, greatly increased in size and 
generally united with its fellow of the opposite side, forming the first 
hypaxial arch. Such arches (figs. 1 & 15) are always present in the 

Under view of anterior caudal vertebree of Menobranchus (No. 5824 in College 
of Surgeons’ Museum). 
ce. Capitular process. Hy. Hypapophysis. 
_ caudal vertebre, except in Siren; but there, though the caudal hypa- 
pophyses remain medianly disunited below, yet each is broad antero- 
posteriorly, as well as much vertically extended (fig. 8, Hy). The 
hypaxial arches are sometimes narrow from before backwards, though 
much elongated from above downwards; this is the case in Meno- 
poma, Cryptobranchus, Menobranchus (fig. 10, Hy), and Proteus. 
In the three first-named genera especially they are produced ob- 
liquely backwards and downwards into long inferior spines, even 
exceeding in length the neural spinous processes above them, and 
are similarly bony cylinders unossified at their summits. In Azolot/ 
and Amblystoma the hypaxial arches repeat the characters offered 
by the neural ones, inasmuch as each is provided with a pair of di- 
verging sockets (fig. 6) apparently for the reception of two cartila- 
ginous spines placed side by side. 
The posterior margin of these hypaxial or hypapophysial arches 

Hy. Hypapophysis. 
is often medianly notched like the corresponding margin of the 
epaxial or neural arches above. This correspondence is often further 
inereased by the frequent development of a median longitudinal 
hypaxial crest, which, bifurcating at the notch, is continued forwards 
