290 REPORT—1846. 
rietal centrum (5). The newral spine of the frontal vertebra (11) retains its 
normal character as a single symmetrical bone, like the parietal spine, which 
it partly overlaps. It is much developed longitudinally, but more in the 
anterior, and less in the lateral direction than in most fishes, 
One cannot contemplate the relative position of the frontal to the parietal 
and of the parietal to the supraoccipital, which is overlapped by the parietal 
and itself overlaps the flattened spine of the atlas, without a conviction of the 
serial homology of these single, median, imbricated bones, all completing 
arches above the neural axis, and each permanently distinct from tie piers 
or haunches of the arch of which it forms the key-stone. In like manner 
the serial homology of those piers or neurapophyses, viz. the lamine of 
the atlas, the exoccipitals, the alisphenoids and the orbitosphenoids, is equally 
unmistakeable. Nor can we close our eyes to the same serial relationship 
of the postfrontals (fig. 20, 12, 12) as parapophyses of their vertebra, with 
the mastoids (s) and the coalesced paroccipitals (4). The frontal parapo- 
physis, 12, is wedged between the back part of the spine, 11, and the neur- 
apophysis, 10: its outward process extends backwards and joins the next 
parapophysis (s); but, notwithstanding the retrogradation of the mandi- 
bular arch, it still receives a small part of its own plewrapophysial element 
(28). This element now manifests its typical unity: vegetative subdivision, 
much reduced in the batrachian reptiles, no more prevails in the develop- 
ment of the frontal pleurapophysis in any higher vertebrate. The serpents 
exhibit this element under the common form of a rib; longer, indeed, than 
are any of the pleurapophyses in the batrachian order; but it has so far 
retreated in serpents as to be exclusively attached to the parietal parapo- 
physis, which is remarkably elongated and produced backwards, and sus- 
pends the long, slender, straight and simple frontal pleurapophysis (tympanic 
pedicle) vertically from its posterior extremity. In lacertians no. 2s is ver- 
tically suspended from no. s, and, commonly also, from no. 27, which is con- 
tinued from the backwardly produced parapophysis of the frontal vertebra 
(12) to that of the parietal vertebra (s) in most of this division of the Cu- 
vierian order Sauria. In chelonians and crocodilians the diverging appen- 
dage of the maxillary arch (27) descends and applies itself to a large propor- 
tion of no. 2s, down to its lower articular end, and contributes to fix and 
strengthen that bone, as well as the modified costal arch from which it di- 
verges. 
The condition of the shortening, expansion and fixation of the frontal 
pleurapophysis in crocodiles and chelonians is exemplified in the uses to 
which the modified heemapophyses, completing that' costal arch, are put. 
Tortoises crop the grass by the application of the trenchant horny plates of 
the under to those of the upper jaw: turtles equally need a fixed suspensory 
joint of the under jaw in the act of biting and dividing the tough sea-weeds. 
Crocodiles have the frontal hemapophyses (mandibular rami) unusually 
long; supporting numerous large laniary teeth, and requiring a fixed and 
firm point of suspension in the violent actions to which they are put in re- 
taining, and overcoming the struggles of their prey. 
The teleological complication of the lower or distal elements of the arch 
in question (29-32, fig. 22) is carried further than in fishes: there was more 
need, in fact, for a combination of the greatest elasticity and strength with 
the least weight of bone* in the frontal hamapophysis of the crocodile than 
in the frontal pleurapophysis of the fish (2s a—2s d, fig. 5). 
There, lastly, remain then in the skull of the crocodile the bones inter- 
* Conybeare, Geol. Trans. 1821, p. 565. Buckland, Bridgewater Treatise, 1836, vol. i. 
p. 176. This author well illustrates the final purpose of the subdivision of the mandibular 
