These are quadrangular, massive, and longer than the vertebræ of other
regions; they decrease in length from the second to the last. The
=third=, =fourth=, and =fifth= are typical, and have the following
characters:
1. The =bodies= are long as compared with those of other vertebræ. Each
presents a median =ventral spine= or =crest=, which becomes more
prominent as it is traced backward, and is tuberculate at its posterior
end. The =lateral aspect= is concave. The =dorsal surface= has a flat
central area which is narrow in the middle of the vertebræ, and wide at
either end; it gives attachment to the superior common ligament. On
either side of this area is a groove which lodges the longitudinal
spinal vein. These lateral grooves are connected at the middle of the
surface by a transverse furrow, in which there are several foramina
through which veins emerge from the spongy substance of the body. The
=anterior extremity= presents a head which has an oval articular
surface, strongly convex, and wider above than below. The =posterior
extremity= is larger and has a nearly circular cotyloid cavity.
[Illustration:
FIG. 8.—LAST CERVICAL AND FIRST THORACIC VERTEBRÆ OF HORSE, LATERAL
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
2. The =arches= are large and strong. They are perforated on either side
by a foramen which communicates with the foramen transversarium. The
vertebral notches are large.
3. The =articular processes= are large. Their articular surfaces are
extensive, oval in outline, and slightly concave; the anterior ones are
directed upward and inward, the posterior downward and outward. The
remaining surface is mainly roughened for ligamentous and muscular
attachment. A crest connects the articular processes of the same side on
the fourth and fifth; on the third it does not reach the anterior
process.
4. The =transverse processes= are large and plate-like. Each arises by
two roots, one from the arch and one from the body; between these is the
=foramen transversarium=, through which the vertebral artery passes. The
process divides externally into anterior and posterior branches, which
are thickened and rough for muscular attachment.
5. The =spinous process= is represented by a crest (Crista spinosa),
which widens behind, and is connected by ridges with the posterior
articular processes.
The =sixth= cervical vertebra has the following distinctive features: It
is shorter and wider than the fifth. The =arch= is large, especially
posteriorly. The =posterior articular= processes are shorter, thicker
and further apart; they are connected with the anterior ones by a thick
ridge. The =spinous process= is less rudimentary; it is half an inch or
more (ca. 1.5 cm.) in height. The =transverse processes= have three
branches; the third part is a thick, almost sagittal plate, which forms
with its fellow and the body a wide ventral groove on the posterior part
of the vertebra; the other branches correspond to those of the typical
vertebræ, but are short and thicker. The =foramen transversarium= is
large; below its posterior end is a fossa. The =ventral crest= is small
and is less prominent posteriorly.
The third branch of the transverse process and the fossa are sometimes
absent on one side.
The =seventh= cervical vertebra is readily distinguished by the
following characters: It is =shorter= and =wider= than the others. The
=body= is flattened dorso-ventrally and wide, especially behind; here it
has a =demifacet= on either side for articulation with part of the head
of the first rib. The =arch= and its =notches= are large. The =anterior
articular processes= are wider and longer than the posterior pair. The
=spinous process= is an inch or more (ca. 3 cm.) in height. The
=transverse process= is undivided, and has no foramen transversarium.
The ventral crest is replaced by a pair of tubercles.
In some specimens a large foramen transversarium is present on one
side or (rarely) on both.
[Illustration:
FIG. 9.—ATLAS OF HORSE, ANTERIOR VIEW. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)
]
[Illustration:
FIG. 10.—ATLAS OF HORSE, POSTERIOR VIEW. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]