128 
O Eld INAL ARTICLES. 
internal to tlie costal arches; but the main trunks of nerve are out¬ 
side these, not on their abdominal aspects, as they would have been 
were August Muller’s theory correct. Hence it appears that the 
costal arches of the higher vertebrata are the same as those of fishes, 
and that the layer of muscle found in their interior is a development 
peculiar to them, which, like various other muscular developments, is 
in fishes not yet separated from the common mass. 
In proceeding to consider the processes continuous in the tail 
with the ribs and transverse processes of the trunk; it is essential to 
bear in mind that where there is no visceral cavity there can 
be no parts entirely corresponding to ribs and transverse processes, 
if the primary characteristic of these parts is their relation to that 
cavity. The importance now becomes apparent of the principles 
formerly laid down, that a single process may be serial with 
more than one row of processes, and that processes in series do 
not necessarily completely correspond. It is thus that, in the 
Mounder and the Conger, the simple transverse processes *in the 
middle of the trunk are continuous with a superior and inferior set 
behind. Were the superior set cut off, we should have the dis¬ 
position met with in most fishes. Were the inferior set cut off, we 
should have left the continuity of the transverse processes of the 
trunk with those of the tail, as found in the other vertebrata. In 
that case there would remain simple processes, the upper parts of 
which would be in the abdominal wall, while their extremities would 
diverge into the intermuscular septum, and so would become radi¬ 
ative. Probably there is not, in the higher vertebrata, any transverse 
process to be found which distinctly presents these relations. The 
transverse processes in the commencement of the Crocodile’s tail 
would exhibit them, if their course were continued outwards as far 
as the skin; but, as it is, they stop short where the lateral inter¬ 
muscular septum separates from the abdominal wall. The trans¬ 
verse processes in the back part of the trunk of the Haddock, how¬ 
ever, afford a good example of processes beginning in the abdominal 
wall and ending in an intermuscular septum radiating outwards. In 
this instance the ribs continue the circle round the abdomen, and in 
the first caudal arch there is a complete circle with processes which 
project from its sides in series with the tips of the transverse pro¬ 
cesses. 
The same relation to the abdominal wall is exhibited in fishes 
which have only the superior set of ribs. In Aspidophorus euro - 
pceus, for example, these bones in the first part of their course bound 
the abdominal cavity, but from the point where the lateral septum 
is given off they quit the abdominal wall and the intercostal nerves, 
and shoot out along the septum to the skin. I have not had an 
opportunity of dissecting Draco , but I apprehend that very similar 
remarks are applicable to its free ribs. 
In Naseus fronticornis, the first caudal vertebra of which is here 
