“cephalic prolongations traversing 
“spine of the nasal vertebra was 
‘cies of alligator I have observed 
ON THE VERTEBRATE SKELETON. 291 
‘sected by the lines N rv and the arrow H rv, with those numbered 26, 27, 
and 73, and we have to inquire whether through all the modifications which 
their extreme position subjects them to, we can still trace any evidence of their 
arrangement according to the vertebrate type. 
A long and slender symmetrical grooved bone, like the ossified inferior 
half of the capsule of a notochord, is continued forwards from the centrum 
of the foregoing vertebra, and stands in the relation of a cenérum (13) to the 
vertical plates of the bones 14, which expand as they rise into the broad and 
thick triangular plates with an ex- : 
posed horizontal superior surface. Fic. 21 
The arch of which these form the My Sar 
piers, and to the anterior rhinen- 
which arch they stand in the re- 
lation of neuwrapophyses, is com- 
pleted by the two bones(13): which 
I, therefore, regard as a divided 
neural spine. In fishes we have 
seen that the corresponding ele- 
ment of the parietal vertebra was 
similarly divided, whilst the neural 
single: in the crocodile the re- 
verse conditions prevail. In a spe- 
the bone 13 continued further for- 
ward, expanded, and divided at the 
middle line, the two divisionsform- 
ing a small disc on the bony palate. 
The centrum of the nasal vertebra 
‘a divid ed longitudinally ue the ane Disarticulated rhinencephalic arch, with the anchylosed 
‘dian line in batrachians, ophidians, pterygoids (24) viewed from behind : Crocodile. 
and most lacertians; it is single in 
‘chelonians, but retains its carti- 
Jaginous ‘state in some species (Emys expansa, e.g.). The neurapophyses 
(14, 14) transmit the olfactory nerves in all reptiles; but the ganglions are 
usually withdrawn backwards into the prosencephalic neural arch, leaving 
ramus in the recent and extinct saurians by pointing out the similarity of the structure to 
that adopted in binding together several parallel plates of elastic wood, or steel, to make a 
cross-bow; and also in setting together thin plates of steel in the springs of carriages. Dr. 
Buckland-adds, ‘Those who have witnessed the shock given to the head of a crocodile by 
the act of snapping together ‘its thin long jaws, must have seen how liable to fracture the 
lower jaw would be, were it composed of one bone‘only on each side.”’—Jb. p. 177. The 
same reasoning applies to the composite condition of the long tympanic pedicle in fishes. 
In each case the splicing and bracing together of thin flat bones of unequal length and of 
varying thickness affords compensation for the weakness and risk of fracture that’ would other- 
wise have attended the elongation of the snout. Inthe abdomen of the crocodile and plesi- 
osaur the analogous composition of the hemapophyses (abdominal ribs) allows of a slight 
change of length in the expansion and contraction of the walls of that cavity: and since 
amphibious reptiles, when on land, rest the whole weight of the abdomen directly upon the 
ground, the necessity of the modification for diminishing liability to fracture further appears. 
‘But what we are here ‘chiefly concerned in is the evidence that ‘the general homology of 
elementary:parts of a natural segment is not affected by the modification of teleological 
composition of such parts. What happens to the hemapopbysial or inferior elements of 
the inverted arch in the abdominal segments of the crocodile also affects the same elements 
of a cranial hemal arch; and the subdivision of the pleurapophyses of the trunk in the 
“stutgeon is repeated in the same elements of the cranial vertebrz in osseous fishes. 
