centrum. In the seventh cervical vertebra, it would appear as if the process were
reversed and the head of the rib were merged in the tubercle.
Erom these facts, regarding the development of the transverse processes of the
cervical region, it would appear that, as they occur in the atlas, axis, and third cervicalj
they are serially homologous with the superior transverse processes of the fourth, fifth,
sixth and seventh cervical vertebrae. The transverse process of the third vertebra is
occasionally, though rarely, perforated by a small foramen on one side, bat its position
is variable. Taking into account the foregoing observations relating to the development
of the processes before us, it is evident that this perforation is adventitious and
no guide to the ultimate nature of the process in question. I t would appear also
that the whole area of the articular surfaces of the atlas and anterior facets of the
n.Tis cannot be regarded as corresponding in position to the points of the attachments
of the heads of the ribs in the thoracic vertebrae, but only to that very limited
section which lies below the detached outer portion of the neurocentral suture;
the superior aspect of those facets being apparently serially homologous with the
pedicles of the succeeding vertebral segments.
In the thoracic region, in the younger foetus, the interval between the laminae
above the spinous processes is cartilaginous. The transverse processes of the first,
second, third, and fourth vertebrae are partially ossified at their bases, more especially so
in the first, but by far the greatest part of them is cartilage; the succeeding transverse
processes of the thoracic vertebrae being wholly cartilaginous, as are also the
posterior zygapophyses. At the eighth vertebra, the pedicles become elevated from off
the side of the centra, till in the eleventh vertebra a wide interval intervenes between
the ossified base of the pedicle and the base of the transverse process. The first
indication of the metapophysis appears on the fifth dorsal. The heads and tubercles
of the ribs are only partially ossified.
In the older skeleton, the first, second, and third laminae are not united, but all the
remaining ones are. The zygapophyses are entirely ossified. The neurocentral suture
is intact in all the vertebrae; in the first four the transverse process is above
the suture, but in the fourth it occupies a much lower pdsition than in the first, the
articular surface from the tubercle of the rib being brought close to the neurocentral
suture in all the dorsal vertebrae, the head of the rib being applied to the neurocentral
suture, so that with the downward removal of the transverse process there
is a corresponding confluence of the head and tubercle of the rib. In the fifth
vertebra, the transverse process is still lower, and its rib facet is distinctly prolonged
on to the neurocentral suture. In the sixth, the confluent tubercle and head of the
rib is applied directly on the neurocentral suture, one-half to the inferior portion
of the pedicle, the remaining half over the neurocentral suture, and portion of the
body of the vertebra. In the seventh, eighth, and ninth, the articular surface from the
rib lies below the neurocentral sutures, being farthest removed from it in the ninth.
In the fifth vertebra, the transverse process is represented by a very slight expansion
of the outer extremity of the lamina and pedicle external to the metapophyses and
immediately above the neurocentral suture. In the sixth, it is still further reduced,
and lying at a considerably lower level below the metapophyses than in the
preceding vertebra and confined to a small surface, which is concave in the adult
fl.nrl situated on the outer basal border of the pedicle. The disappearance of the
superior transverse process in the thoracic region is very gradual, and is completed
in the seventh vertebra, where the rib-bearing process is wholly central. In the
succeeding vertebrae, the process is very rudimentary, but it increases in lateral
extension to the ninth. In all of these, it is an exogenous product of the centrum,
and thus differs in its development from the superior transverse processes of the
neck. When there are ten ribs the last is generally articulated to two transverse processes
by its head to the autogenous transverse process of the tenth vertebra, and by its
angle to the much larger similar transverse process of the first lumbar vertebra. In
the third skeleton already referred to, the neurocentral suture is intact in all the
dorsal vertebræ, save the last, in which, and in all the remaining neural arches, it has
amalgamated with its centrum, although the remains of it can be traced in the
last dorsal, in all the lumbar vertebræ, and in the first three caudals, its
union with the centra being most complete in the terminal six caudal vertebræ.
The transverse processes of the lumbar region are also autogenous products, and in
the younger skeleton they are all ossified, but quite distinct at their bases from the
centra, and broadly tipped with cartilage. The neural arch is even at a still higher
level on the bodies than in the last dorsal vertebra, and they are quite distinct from
each other,, none of them articulating by zygapophyses. The metapophyses are
short and abruptly truncated, their tips being cartilaginous. The laminæ are also
separated by a cartilaginous interspace. In the older foetus, the neurocentral suture
is intact, as are also all the sutures at the bases of the transverse processes, which
in the case of the first to the fourth lumbar disappear at a later period than all
the others, and then the neurocentral, as illustrated by the condition of these
parts in the third and oldest skeleton. In the former, or second skeleton, the
metapophyses are strongly developed and overlap the vertebræ, and the zygapophyses
are perfect.
In the caudal region, only the first transverse processes axe ossified, but a small
cdnla can be detected in the fourth and fifth; all the remaining processes are
wholly cartilaginous. The third transverse process, on either side, has the remarkable
character, that it is developed from two ossific centres, the one next the centrum being
the larger and the distal one the smaller. In the right side, the ossicles axe perfectly
distinct, whereas on the left, in which they are much more developed, they have
partially united. This arrangement exactly simulates the condition of things
found in the last dorsal Vertebra, in which the rib is developed at the extremity
of its autogenous transverse process. The ossicles of the chevroii bones axe
developed as far back as the fourteenth in the youngest specimen, but. in the
third and oldest skeleton they can only be traced the same distance;;fit is evident,
therefore, that all the remaining chevrons are developments of after-life, as the
mother of the former specimen had twenty-two such structures. ‘ The ossicles
occur as little round plates on the sides of the cartilaginous arches. The neural