MR. W. K. PARKER ON THE OSTEOLOGY OF BALZNICEPS REX. 329 
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 
vertebree, 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—sometimes first expanding so as wholly to enclose 
it ; as, for example, in the Tunny, where the line of demarcation may always be seen at 
the border of the articular concavity, though it is quite obliterated at the centre, as a 
section through that part demonstrates.” Again, page 256 :—“ In saurians, birds, and 
mammals, the notochord is enclosed by cartilage before ossification begins, which car- 
tilage is continuous with the cartilaginous neurapophyses. In birds, the two histological 
processes, chondrification and ossification, do not precisely follow the same route. In 
the centrums of the dorsal and cervical vertebra of the Chick chondrification is centri- 
petal: it begins from two points at the sides, and proceeds inwards, the middle line of 
the under surface of the primitive notochord resisting the change longest. But, when the 
lateral cartilages have here coalesced, ossification begins at the middle line and diverges 
laterally ; the primitive nuclei of the bony centres appearing as bilobed ossicles, and 
its direction is centrifugal. The lobes ascend to embrace the shrivelled remnant of the 
chorda, like the hollow vertebral centres in fishes. Only in the sacral vertebre has 
ossification been seen to begin from two distinct points at the middle line. The bases 
of the separately ossifying neurapophyses extend over much of the centrum, and soon 
coalesce with it.’’ Remark here, that the carotid canals are formed by exogenous mar- 
ginal processes from the lower centre of ossification. We must be allowed to make 
another quotation. Speaking, in page 260, of the development of the anterior vertebre 
of ‘a large South American siluroid fish,’ which has ‘the first five centrums rigidly 
fixed together by continuous ossification below,’ although ‘ the concave articular cavities, 
with the elastic capsules and contained fluid,’ were seen in a vertical section, Professor 
Owen says, ‘‘ The continuous bony plate supporting those centrums was perforated 
lengthwise by the aorta, offering another mode of the formation of a hemal canal—viz. 
by exogenous ossification in and from the lower part of the outer layer of the capsule 
of the notochord ; the carotid hemal canal in the necks of birds seems to be similarly 
formed ; and the neck of the Ichthyosaurus derives additional strength and fixation 
from apparently detached developments of bone in the lower part of the capsule of the 
notochord, at the inferior interspace between the occiput and atlas, and at those of two 
or three succeeding cervical vertebra.” 
Note.—The odontoid process of the mammalian axis is considered by our author to 
belong to the same category'; but in that delightful little work of his on ‘ The Nature 
of Limbs’ (1849), this ossific centre is described as the main or internal part of the 
centrum of the atlas, whilst the basal part of the atlas is considered to be the cortical 
or hypapophysial portion of that bone. See pages 94, 107, and 112. 
' See page 261 of the same Report. 
