266 © REPORT—1846. 
_'The neural spine commonly retains in the trunk the form indicated by its 
name ; but in the atlas of the crocodile, where it is distinct from the neur-. 
apophyses, it isa depressed plate. In the thorax and abdomen of chelonians 
it becomes still more expanded and flattened, and its borders unite by dentated. 
suture to contiguous spines and to the similarly expanded pleurapophyses. 
The neural spine is absent in the thin annular cervicals of the mole; it is 
unusually developed and forms a thick square columnar mass of bone in the 
cervicals of the opossum. It is double in the anterior vertebrze of some 
fishes: in the barbel one stands before the other; in the tetrodon they 
stand side by side: and various other minor modifications of this peripheral 
element might be cited, 
The parapophyses of the trunk-vertebre manifest their autogenous cha- 
racter in fishes alone; andin most species the character is soon lost, the par- 
apophyses becoming confluent with the centrum ; and, in the tail, either with 
the pleurapophyses also, or with each other and the hzmal spine, thus comple- 
ting the hemal canal (fig. 16). Amongst air-breathing vertebrates the par- 
apophyses of the trunk-segments are present only in those species in which 
the septum of the heart’s ventricles is complete and imperforate, and here. 
they are exogenous and confined to thecervical and anterior thoracic vertebree, 
or to the sacrum (as in the ostrich, figs. 15 and 27, p). The parapophyses are 
subject to a certain extent of variation as to form: they are either mere 
tubercles; or simple, shorter or longer, transverse processes ; or they may take 
the form of long plicated laminz (in the tails of some pleuronectidz): they 
are longer and broader than the pleurapophyses in the cod-tribe ; and are 
sometimes much expanded in the anterior vertebre of fishes, where they 
ascend in position, and in the siluroid species above described, coalesce to 
iorm a broad outstanding ridge, directed outwards and a little upwards, and 
rising as they approach the cranium, where they are joined by close suture to 
the paroccipitals. 
The normal function of the parapophyses is to give attachment to muscles 
and articulation to ribs, and, occasionally, additional strength and fixation to 
anchylosed portions of the vertebral column, As a rare and exceptional in- 
stance, the expanded and excavated parapophyses of the second and third 
vertebra in the genus Cobitis perform an office closely analogous to one of 
those of the mastoid in man, since they inclose air-cells brought into com-. 
munication with the acoustic labyrinth by a chain of small ossicles : and these 
singularly modified rudiments of the swim-bladder seem to have no other func- 
tion in the groveling loaches than that in connection with the sense of hearing. 
The pleurapophyses are less constant elements than the neurapophyses ; 
they exist as free appendages or ‘ floating vertebral ribs’ in the trunk, and 
sometimes at the fore-part of the tail, in fishes, serpents, and certain batra- 
chians (fig. 28, pl). The atlas has its pleurapophyses in most fishes, but they. 
are often detached from their centrum, and sometimes joined to long bony 
hzmapophyses, as is well-seen in the Argyrecosus, and other deep-bodied 
scomberoids. Ossified heemapophyses are not present in any other vertebra 
of the trunk in fishes. In batrachians the pleurapophyses of the single pelvic 
vertebra are similarly connected with hamapophyses, and the costal arch is, 
there completed.’ In the menopome, the pleurapophysial element of the sacrum, 
ib. pl', is ossified from two centres. Such typical vertebrae are more common 
in the higher air-breathing classes. Here the pleurapophyses have generally 
the long and slender form understood by the word ‘rib ;’ but they expand into 
broad plates in the thorax of the apteryx, in the anterior thoracic vertebra of 
whales, and more especially in the carapace of chelonians, where they are 
joined to each other by suture, and also to the expanded neural spines. These. 
