See. 
a ney 
2 
Mi 
4 
: 
4 
a 
“A 
: 
4 
ON THE VERTEBRATE SKELETON. | 285 
-“The scapulo-coracoid arch, both elements of which retain the form of 
‘strong-and thick vertebral and sternal ribs in the crocodile, is applied in the 
skeleton of that animal over the anterior thoracic hemal arches. Viewed 
as a more robust heemal arch, it is obviously out of place in reference to the 
rest of its vertebral segment. If we seek to determine that segment by the 
‘mode in which we restore to their ceutrums the less displaced neural arches 
‘in the sacrum of the bird (fig. 27, m 1-7 4), we proceed to examine the verte- 
bre before and behind the displaced arch with the view to discover the one 
which needs it in order to be made typically complete. Finding no centrum and 
neural arch without its pleurapophyses from the scapula to the pelvis, we give 
‘up our search in that direction ; and in the opposite direction we find no verte- 
“bra without its ribs until we reach the occiput: there we have centrum and 
neural arch, with coalesced parapophyses—the elements answering to those 
included in the arch N 1, fig. 5—but without the arch H1; which arch 
can only be supplied, without destroying the typical completeness of antece- 
dent cranial segments, by a restoration of the bones 50-52, to the place which 
they naturally occupy in the skeleton of the fish. And since anatomists 
“are generally agreed to regard the bones 50-52 in the crocodile (fig. 22) 
as specially homologous with those so numbered in the fish (fig. 5), we 
must conclude that they are likewise homologous in a higher sense ; that in 
fig. 5 the scapulo-coracoid arch is in its natural or typical place, whereas in 
the crocodile it has been displaced for a special purpose. Thus, agreeably 
with a general principle, we perceive that as the lower vertebrate animal 
‘illustrates the closer adhesion to the archetype by the natural articulation of 
the scapulo-coracoid arch to the occiput, so the higher vertebrate manifests 
the superior influence of the antagonising power of adaptive modification by 
the removal of that arch from its proper segment. 
The scapula retains the more common cylindrical long and slender rib- 
like form of the pleurapophysis in the chelonian reptiles, where, from the 
- greater length of the neck, it has retrograded further than in the crocodile 
‘from its proper centrum, and is placed not upon, but within, an anterior 
thoracic hemal arch, the pleurapophysis of which has, on the other hand, 
been expanded like a scapula. 5 
If the arguments founded upon the relations of the scapulo-coracoid arch 
to the segments of the skeleton in osseous fishes and crocodilians be admitted 
“to sustain the conclusion here drawn from them, that arch must be held to 
form the hemal complement of the occipital vertebra in all animals. Bojanus, 
in illustrating his vertebral theory of the skull by the osteology of the Eimys 
. Europea, thus defines the 
g J “ VERTEBRA OCCIPITALIS, SIVE CAPITIS PRIMA. 
' “Basis occipitis, seu corpus hujus vertebra, 
~~ Pars lateralis occipitis, sive arcus, 
“Crista occipitalis, processus spinosi loco, 
“ Cornu majus hyoidis, coste vertebre occipitalis comparandum *,” 
He adds a dotted outline of the hyoid arch to complete the vertebra oc- 
cipitalis, in tab. xii. fig. 32, B. 1 of his beautiful Monograph. 
Supposing the special homology of the middle cornua of the hyoid of the 
chelonian, so represented and compared to ribs by Bojanus, with the stylo-, 
epi- and cerato-hyals of the fish (fig. 5, 38, 39,40) to have been correct, which 
the metamorphoses of the hyoid and branchial arches in the batrachians dis- 
» prove, the singular and highly interesting change of position as well as shape 
of the true ceratohyals, during the same metamorphosis, prepares us to expect 
_aretrogradation of the hyoid arch in respect to its proper centrum, in the 
* Anatome Testudinis Europzz, fol, 1819, p. 44. 
