st of the transverse process; and the form of the
equivalent structures in certain peculiar lower mammals and in
reptiles leaves no doubt that f.r. is really an abbreviated rib; fused up
with the transverse process and body. The two anterior cervical
vertebrae are peculiar. The first (at.) is called the Atlas-- the figure
shows the anterior view-- and has great articular faces for the
condyles (Section 86) of the skull, and a deficient centrum. The next
is the axis, and it is distinguished by an odontoid peg (od.p.), which
fits into the space where the body of the atlas is deficient. In
development the centrum of the axis ossifies from one centre, and the
odontoid, peg from another, which at that time occupies the position
of centrum of the atlas. So that it would seem that the atlas is a
vertebra minus a centrum, and the axis is a vertebra plus a centrum,
added at the expense of the atlas.

Section 79. The lumbar vertebrae (l.v.) are larger, and have cleft
transverse processes, each giving rise to an ascending limb, the
metapophyses, and a descending one. The latter (generally spoken of
as the transverse processes) point steeply downward, and are
considerably longer than those of thoracic series. The sacral
vertebrae (s.v.) have great flattened transverse propcesses for
articulation with the ilia. The caudal vertebrae (c.v.) are gradually
reduced to the mere elongated centra, as we proceed, towards the tip
of the tail.

Section 80. All the vertebrae join with their adjacent fellows through
the intermediation of certain intervertebral pads, and also articulate by
small processes at either end at the upper side of the arch,
the zygapophyses. The normals to the polished facets of these point,
in the case of the anterior zygapophyses, up and in (mnemonic:
ant-up-in), and in the case of the posterior, down and out. The student
should make this, and the other features of vertebrae, out upon actual
specimens.

Section 81. The thorax is bounded dorsally by the vertebral column,
and ventrally by the sternum. The sternum consists of segments,
the sternebrae (st.); anteriorly there is a bony manubrium (mb.),
posteriorly a thin cartilaginous plate, the xiphisternum (xi.). Seven
pairs of ribs articulate by cartilaginous ends (sternal ribs) with the
sternum directly, as indicated in the figure; five (false) ribs are joined,
to each other and to the seventh, and not to the sternum directly.
The last four ribs have no tuberc