256 REPORT—1846. 
two neurapophyses and the two parapophyses ; but the terminal concave plates 
of the centrum are separately ossified. They coalesce with the intermediate 
part of the centrum, which is sometimes completely ossified, but commonly a 
communicating aperture is left between the two terminal cones; and in 
many cases, the plates by which calcification attains the periphery of the 
body leave interspaces permanently occupied by cartilage, forming cavities 
in the dried vertebra, especially at their under part, or giving a reticulate 
surface to the sides of the centrum. ‘The expanded bases of the neur- and 
par-apophyses usually soon become confluent with the bony centrum; some- 
times first expanding so as wholly to inclose it, as, for example, in the tunny, 
where the line of demarcation may always be seen at the border of the arti- 
cular concavity, though it is quite obliterated at the centre, as a section 
through that part demonstrates. 
Miller correctly distinguishes a ‘central’ from a ‘peripheral’ (cortical) part 
or seat of the ossification of the vertebral bodies of fishes. The peripheral 
ossification which takes its rise from the outer layer of the fibrous sheath of 
the notochord sometimes extends into broad plates beneath the anterior ver- 
tebree of the trunk, and tends to fix or anchylose a certain number of them; 
when they are commonly represented by the partially distinct central parts 
of the bodies, together with the neur- and par- and pleur-apophyses. 
The batrachia follow closely the stages above-cited in fishes ; the centrums 
being arrested at the biconical stage in the perennibranchiates, but converted 
into ball-and-socket vertebr by the ossification of the interposed gelatinous 
ball* and its adhesion, either to the fore-part of the centrum (Pipa, Sala- 
mandra), or the back part (Rana, Bufo). The mode of ossification of the 
centrum varies somewhat in batrachia. Miullert describes annular ossifi- 
cations in the sheath of the notochord of the Rana temporaria and R. escu- 
lenta, which support, at first, the neurapophyses. Dugés, apparently in- 
fluenced by M. Serres’ so-called ‘law of centripetal development,’ describes 
two cartilaginous nuclei, side by side; but the more obvious and better-de- 
termined development of the vertebrz of fishes gives no countenance to this 
bilateral beginning of ossification of the centrum as a general law. The first 
distinct bony nucleus in the centrum observed by Dugés was bilobed, and 
afterwards cubical; but excavated before and behind, as well as beneatht. 
The ossification of the centrum is completed by an extension of bone from 
the bases of the neurapophyses, which effect, also, the coalescence of these 
with the centrum. In Pelobates fuscus, and Pelobates cultripes, Miller found 
the entire centrum ossified from this source, without any independent points 
of ossification. 
The vertebrz of the tail of the larve of the anourans are represented di- 
stinctly only in the aponeurotic stage. Even when the change to cartilage 
takes place, the tendency to coalescence has begun to operate, and only two 
long neurapophyses are established on each side: the ossification of these 
plates extends into the fibrous sheath of the remnant of the coccygeal noto- 
chord, and they coalesce when the perishable parts of the tadpole-tail have 
been absorbed, and the fore- and hind-legs developed, constituting the long, 
often hollow, and inferiorly grooved coccygeal bony style. 
In saurians, birds and mammals, the notochord is inclosed by cartilage 
before ossification begins; which cartilage is continuous with the cartilagi- 
nous neurapophyses§. In birds, the two histological processes, chondrifica- 
* Duirochet, Mémoires pour servir a l’Histoire Nat. et Physiol. des Animaux, &c., t. ii. 
p- 302. 1837. 
+ Neurologie der Myxinoiden, 1840, p. 69. 
t Recherches sur les Batraciens, 1835, 4to, p. 106. 
§ Muller, Vergleichende Anatomie der Myxinoiden, Neurologie, 1840, p. 74. 
