i 
: 
ON THE VERTEBRATE SKELETON. 287 
might reply, to neither. And such, doubtless, would be the matter-of-fact 
answer most congenial to the character of mind which would limit its views 
to the specialities of the ribs as parts independent of any ideal archetype, or 
be unable or unwilling to push the consideration of their connections beyond 
the purposes apparently subserved thereby. A second anatomist might see 
in the more constant articulation of the costal tubercle with the transverse 
process, a character which would incline the balance in favour of the vertebra 
to which the transverse process belonged. A third anatomist might extend 
his comparisons to other ribs and centrums, and finding the lower centrum 
obtaining by degrees a greater proportion of the head of the rib, until the 
first and last ribs respectively wholly articulated to the centrum answering to 
the lower one in the case of the hypothetically detached sixth pair, he would 
conclude that such pair of ribs belonged essentially to the lower and not 
to the upper supporting centrum, and he would count accordingly such 
lower centrum with its neural arch, as the sixth of those vertebrze which are 
characterized as supporting ribs. The anthropotomist, in fact, in so counting 
and defining the dorsal vertebre and ribs, admits unconsciously perhaps, an 
important principle in general homology, which pursued to its legitimate 
consequences and further applied, demonstrates that the scapula is the modi- 
fied rib of that centrum and neural arch which he calls the ‘ occipital bone,’ 
and that the change of place which chiefly masks that relation (for a very 
elementary acquaintance with comparative anatomy shows how little mere 
form and proportion affect the homological characters of bones) differs only 
in extent and not in kind from the modification which makes a minor amount 
of comparative observation requisite in order to determine the relation of the 
shifted sixth 1ib to its proper centrum. 
With reference, therefore, to the occipital vertebra of the crocodile, if the 
comparatively well-developed and permanently distinct ribs of all the cervical 
vertebre prove the scapular arch to belong to none of those segments, and, 
if it be wanting to complete the occipital segment, which it actually does 
complete in fishes, then the same conclusion must apply to the same arch in 
other animals, and we must regard the occipital vertebra of the tortoise as 
«completed below by its scapulo-coracoid arch, and, not as Bojanus supposed, 
by its hyoidean arch*. 
With these views of the general homology of the scapulo-coracoid arch, 
the embryologist will observe with less surprise its constant appearance in 
the first instance close to the occiput, and its equally constant primitive ver- 
‘tical position; however far back it may be subsequently removed, or to 
whatever extent it may be rotated, in the same progress to maturity, out of 
its original parallel direction with the more normal pleurapophyses. 
Returning to.the study of the crocodile’s skull in reference to the verte- 
brate archetype, if we proceed to dislocate the next segment in advance of 
the occipital, we bring away in connection with the long base-bone, 5 and 9, 
fig. 22, the bones connected by the double lines N11, N 111, and by the 
* Geoffroy St. Hilaire selected the opercular and subopercular bones to form the inverted 
arch of his seventh (occipital) cranial vertebra (Table III. and note 11), and took no account 
of the instructive natural connections and relative position of the hyoidean and scapular 
varches in fishes. With regard-to the scapular arch, he alludes to its articulation with the 
_skull:in the lowest of the vertebrate classes as an ‘ amalgame inattendue’ (Anatomie Philo- 
sophique, p..481); and elsewhere describes it as a ‘‘ disposition véritablement trés singuliére, 
et que le manque absolu de cou et une combinaison des piéces du sternum avec celles de la 
téte pouvoient seules rendre possible.”—Annales du Muséum, ix. p.361. A due appre- 
ciation of the law of vegetative uniformity or repetition, and of the ratio of its prevalence 
and power to the grade of organization of the species, might have enabled ‘him ‘to discern 
the true signification of the connection of the scapular arch in fishes. 
