_a_, Cranium; _b_, upper jaw; _c_, lower jaw; _1H.-7H._, cervical
vertebræ; _1R.w._, first thoracic vertebra; _13 R.w._, thirteenth
thoracic vertebra (next to last); _1L._, first lumbar vertebra;
_6L._, sixth lumbar vertebra (next to last usually); _K._, sacrum;
_S._, coccygeal vertebra; _1R._, first rib; _14R._, last rib;
_R.kn._, costal cartilages; _St._, sternum; _d_, supraspinous fossa
of scapula; _d′_, infraspinous fossa; _1_, spine of scapula; _2_,
neck of scapula; _e_, humerus; _3_, head of humerus; _4_,
tuberosities of humerus; _5_, deltoid tuberosity; _6_, external
epicondyle of humerus; _f_, radius; _g_, ulna; _7_, olecranon; _h_,
carpus; _18–25_, carpal bones; _i-i⁗_, metacarpus; _k-k⁗_, proximal
phalanges; _l-l⁗_, middle phalanges; _m-m⁗_, distal phalanges; _n_,
_o_, sesamoids; _p_, ilium; _8_, external angle of ilium (tuber
coxæ); _9_, internal angle of ilium (tuber sacrale); _10_, superior
ischiatic spine; _q_, ischium; _11_, tuber ischii; _r_, pubis; _12_,
acetabulum; _s_, femur; _13_, trochanter major; _14_, trochanter
minor; _15_, external epicondyle; _t_, patella; _u_, tibia; _16_,
crest of tibia; _17_, external condyle of tibia; _v_, fibula; _w_,
tarsus; _26–31_, tarsal bones; _26′_, tuber calcis. (After
Ellenberger, in Leisering’s Atlas.)
]
The =cervical vertebræ= are short and wide. The bodies are elliptical in
cross-section, the long diameter being transverse. The anterior
articular surfaces are slightly convex from side to side and concave
dorso-ventrally; the posterior ones are slightly concave. A ventral
crest is not present. The arches are wide from side to side, but the
laminæ are narrow, so that a considerable interval (Spatium
interarcuale) separates adjacent arches dorsally. The pedicles are
perforated by a foramen on either side in addition to the usual
intervertebral foramina. The transverse processes divide into two
branches, both of which increase in size from the third to the sixth.
The upper branch projects outward and backward; it is short and is
thickened at its free end. The lower branch is a quadrilateral plate
directed ventrally; each overlaps the succeeding one to a small extent,
and the series forms the lateral boundary of a deep and wide groove
beneath the bodies. The spines increase in height from the third to the
last; the anterior ones are inclined backward, the posterior ones
forward. The last cervical is recognized by the great length of its
spine (ca. 10 cm. in the adult), the absence of the ventral plate of the
transverse process, and the flatness of the body, which bears a pair of
small facets on its posterior margin for the heads of the first ribs. It
has foramina transversaria, and usually two foramina in either side of
the arch.
The dorsal arch of the =atlas= bears a large tuberosity. The ventral
tubercle is long, compressed laterally, and projects back under the
axis. The wing is flattened and bears a posterior tuberosity. The
foramen transversarium passes through the posterior border of the wing
to the fossa under the latter, and is not visible dorsally; it is
sometimes very small or absent. The sides of the vertebral foramen bear
two lateral projections which partially divide it into a ventral narrow
part, which receives the odontoid process, and a dorsal larger part for
the spinal cord. In the fresh state the division is completed by the
transverse ligament, which is attached to the projections.
The =axis= has a large spinous process, which is directed upward and
backward. The odontoid process is a thick cylindrical rod. The
transverse process is very small and the foramen transversarium is often
incomplete.
[Illustration: