CLELAND ON RIBS AND TRANSVERSE PROCESSES. 121 
distinguishing them as a different order of processes from those in 
front, with which they form a continuous series. 
August Muller, in a highly* elaborate paper, concludes that the 
ribs embracing the abdominal cavity in fishes are peculiar to that class 
of animals, and that the ribs of the other vertebrata correspond to 
the bones, in fishes, which lie in the lateral intermuscular septum, 
differing from them only in being prolonged beneath the skin to the 
middle line below, so as to embrace those muscles which are equi¬ 
valent to the mass lying below the lateral intermuscular septum in 
the fish. He therefore recognises two sets of transverse processes 
and two sets of ribs, but the division into rib and transverse process 
he considers, and indeed proves, to be of very secondary importance. 
The rays which in certain fishes are found in the flesh, above and 
below the middle lateral line, he allows to be secondary. To this 
theory we must return. 
Professor Owenf recognises two sets of transverse processes, the 
parapophyses and the diapophyses: but he only admits one set of 
ribs or pleurapopbyses ; and these may be connected with either the 
parapophyses or diapophyses, and may either strike outwards or be 
interpolated between their supporting processes and the hsemapo- 
physes. Thus the only constant characteristic which seems to belong 
to them, is that they are ossifications distinct from the vertebral pro¬ 
cesses which support them. They form a very distinct part of the 
conception of a typical vertebra, as laid down by the learned Professor; 
and one understands at once the part which in their character of an 
ideal element they are supposed to play ; but the difficulty is, in the 
application of the conception, to say what characters shall constitute 
the claim of a particular process, or part of a process, to be considered 
pleurapophysial. This is more especially the case, as Professor Owen 
recognises that the source of ossification of a structure is indeed of no 
primary significance, speaking as he does of “ connation” and “coal¬ 
escence” of elements. Thus, speaking of a vertebra from the tail of a 
Serpent, he says: “All the parts are coalesced into one bone: the pleu- 
rapophyses appear as short deflected extremities of long diapophyses. 
Again, describing the skeleton of a Dugong, he says: “ There are 
19 dorsal vertebrae, but the 19th pair of ribs are much shorter, 
* Beobachtungen zur vergleichenden Anatomie der Wirbelsaiile. Muller’s Ar- 
chiv. 1853, pp. 260-315. My attention was first drawn to this paper by Professor 
Goodsir, in his summer courses of lectures on Comparative Anatomy. The same theory 
presented itself independently to his mind before he had seen August Muller’s paper. 
But whatever his sentiments may have been with regard to it, he has not extended 
to it the support of his published opinion, and I only mention these circumstances, 
because having thus seen that many arguments could be brought forward in favour 
of August Muller’s theory, I have been led the more fully to take it into considera¬ 
tion now. 
f On the Archetype and Homologies of the Vertebrate Skeleton. The disposi¬ 
tion of the pleurapophyses is given at p. 99. 
f Descriptive Catalogue of Osteological Series in the Museum of the College of 
Surgeons, Vol. i. p. 6, No. 26. 
