1870. | AXIAL SKELETON OF THE URODELA. 277 
of the neural arch with the body) a large concave articular surface 
which receives one of the projecting articular processes or condyles 
of the posterior end of the skull. Moreover the median part of the 
vertebra, instead of presenting either a concavity (like the hinder 
Fig. 18. 

Dorsal view of first four vertebrx of Siren (No. 5768 in College of Surgeons’ 
Museum), 
surface) or a rounded articular ball (like that always present in the 
other vertebrae of Opisthoccelous forms such as Salamandra, Triton, 
&e.) exhibits between the two anterior large articular concayities a 
small or considerable median process* (fig. 19). This projects for- 
wards and fits into a recess at the base of the skull between the two 
posterior (occipital) condyles, and generally bears on each side of it 
a small articular facet; but sometimes these two facets are united 
into one continuous articular surface on the inferior aud infero-lateral 
aspects of the process. 

Lateral, dorsal, and under view of first vertebrx of Amphiuma (No. 579 4 in 
Museum of College of Surgeons). 
This azygos part attains its maximum of development in Amphiuma. 
It is small in Axoloél, but at its minimum in Menobranchus and 
Proteus, especially the latter. As far as I have observed or been 
informed, no bony or cartilaginous part is ever developed between 
the neural arch of the cervical vertebra and the skull; that is to 
say, if this cervical vertebra is really the axis, then the neural arch 
of the atlas vertebra of higher vertebrates is quite absent in the 
Urodela. The size of the cervical vertebra, as compared with that 
of succeeding vertebre (e. g. with the third) varies somewhat. 
In most cases the two vertebrae are of nearly equal length and 
size; but in Amphiuma the cervical vertebra is rather smaller than 
the third; and it is much so in Menobranchus and Proteus, in the 
last especially, where it is very remarkable for its small size. 
* It is the presence of this process which renders it probable that the cervical 
vertebra is an axis vertebra, and not an atlas one. 
