_1_, Dorso-lateral coccygeal vessels and nerve; _2_, ventro-lateral
coccygeal artery and nerve; _3_, middle coccygeal artery; _4_,
sacro-coccygeus superior; _4′_, sacro-coccygeus lateralis; _5_,
_5′_, intertransversales; _6_, sacro-coccygeus inferior; _7_,
recto-coccygeus; _8_, coccygeal fascia; _9_, fibro-cartilage between
fourth and fifth coccygeal vertebra. The veins are black.
]
3. The =lateral sacral artery= (A. sacralis lateralis) arises at the
lumbo-sacral articulation (Fig. 451). It passes backward under the wing
of the sacrum, then along the pelvic surface of the bone below the
inferior sacral foramina and the nerves emerging from them, and is
continued by the lateral coccygeal artery. The branches are as follows:
(1) =Spinal branches= (Rami spinales) enter the vertebral canal through
the foramen between the last lumbar vertebra and the sacrum and through
the ventral sacral foramina. They give off branches to the spinal cord
and its membranes which reinforce the ventral spinal artery, and others
which emerge through the dorsal sacral foramina and supply the muscles
and skin of the croup.
(2) The =middle coccygeal artery= (A. coccygea) is an unpaired vessel
which arises from the right or left lateral sacral or from a lateral
coccygeal artery. It passes backward on the pelvic surface of the sacrum
to the median line and continues in that position along the tail between
the depressor muscles, supplying these and the skin.
[Illustration:
FIG. 455.—DISSECTION OF PELVIS, THIGH, AND LEG OF HORSE, EXTERNAL
VIEW.
_1_, Dorsal branches of last intercostal and first three lumbar
nerves; _2_, cutaneous branch of fourth lumbar nerve; _3_, ventral
branches of last intercostal nerve: _4_, branches of
ilio-hypogastric nerve; _5_, superficial branch of ilio-inguinal
nerve; _6_, great sciatic nerve; _7_, _8_, nerves to biceps femoris
(from posterior gluteal nerve); _9_, nerve to semitendinosus (from
same); _10_, posterior cutaneous nerve of thigh; _11_, internal
pudic nerve; _12_, anterior gluteal vessels and nerves; _13_,
posterior gluteal (or ischiatic) vessels; _14_, branches of
obturator vessels; _15_, proximal muscular branches of great sciatic
nerve to biceps femoris, semitendinosus, and semimembranosus; _16_,
nerve to tensor fasciæ latæ (from anterior gluteal nerve); _17_,
gluteus profundus; _18_, stump of gluteus medius; _19_, gemellus;
_20_, trochanter major; _21_, stump of biceps femoris; _22_,
sacro-coccygeus superior; _22′_, sacro-coccygeus lateralis; _23_,
coccygeus; _24_, sacro-coccygeus inferior; _25_, line of fusion of
aponeuroses of internal and external oblique muscles of abdomen;
_25′_, aponeurosis of external oblique muscle (lamina iliaca); _26_,
branches of iliaco-femoral vessels; _27_, ilio-lumbar vessels; _28_,
ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; _29_,
external angle of ilium; _30_, internal angle of ilium; _31_,
lateral sacro-iliac ligament; _32_, sacro-sciatic ligament. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
(3) The =posterior gluteal= or =ischiatic artery= (A. glutea caudalis)
emerges through the upper part of the sacro-sciatic ligament and runs
backward and downward on the latter under cover of the biceps femoris
(Fig. 455). It gives branches to that muscle and to the semitendinosus
and semimembranosus, and anastomoses with the obturator, deep femoral,
and posterior femoral arteries.
(4) The =lateral coccygeal artery= (A. caudalis lateralis ventralis)
continues the direction of the lateral sacral, but is much smaller than
the preceding vessel. It passes back between the depressor and
intertransversales muscles of the tail and divides into two branches
which supply twigs to the muscles and skin.
4. The =ilio-lumbar artery= (A. iliolumbalis) arises at a right angle
from the internal iliac and runs outward behind the sacro-iliac joint,
crossing the ventral surface of the ilium under cover of the iliacus
muscle. It gives branches to the ilio-psoas and longissimus, and
terminates by turning around the external border of the ilium a little
behind the external angle, giving branches to the gluteus medius and
tensor fasciæ latæ (Fig. 455).
[Illustration: