1870. ] AXIAL SKELETON OF THE URODELA. 273 
the rib beyond the point from which it starts (figs. 11 & 12). In 
this case the rib may be truly said to bifureate distally. 

Lateral view of sixth vertebra of Salamandra (No. 5898 in Museum of College 
of Surgeons), showing rib bifurcating at each end. 
ec. Capitular process. ¢. Tubercular process. 
A similar process is also sometimes developed from the same part 
of the ribs next succeeding ; but it is rarely to be traced beyond the 
fourth pair of ribs, and diminishes in size as we proceed from before 
backwards, and in many forms is not to be detected at all, as far as 
I have observed, e. g. Menopoma, Cryptobranchus, Menobranchus, 
Aneides, Spelerpes rubra, and Plethodon. 
Though, as has been said, the ribs of the opposite side are never 
connected together by hard parts, but only by membranous prolon- 
gations, yet in the middle line of the anterior part of the body there 
is in many Urodela a solid structure answering to the sternum of 
higher animals, and connected with the membranous prolongations 
of the ribs. 
Tue STERNUM. 
This part is a constant structure in adult Urodela, except in Pro- 
teus, Menobranchus, and perhaps Siren. It is rhomboidal in shape, 
about as broad as long, and with an apex turned forwards. Some- 
times, e. g. Salamandra, there is a short xiphoid process, which ex- 
tends backwards from the middle of its hinder margin. Rarely (e. g. 
Azolotl) that margin is medianly notched. 
Each side of the sternum is more or less deeply grooved for the 
reception of the coracoid lamella, and the inner lip of each groove is 
much more developed than the outer one. 
The sternum never ossifies in any Urodele, and originally it is 
always formed within the coracoids. This might be expected to be 
the case from the fact that the sternum is a portion of the paraxial 
skeletal system which the pectoral girdle externally surrounds. But 
Mr. Parker* has actually verified by observation this primitive con- 
dition of the sternum, and proved that the lateral parts of the struc- 
ture, which embrace the coracoid lamellze externally, are subsequent 
and secondary outgrowths of a structure which is at first completely 
internal to the shoulder-girdle. These secondary growths are so 
large that ultimately the sternum comes to lie outside the coracoids +. 
* See ‘Shoulder-girdle,’ p. 65, : 
t Parker, 7. c. pl. 3, fig. 14. 
