Page 156 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Muscular System / 141

They include the m. biceps femoris median plane. The deep gluteal muscle
(m. gluteus profundus) extends from the
(the most lateral of the caudal muscles of
VetBooks.ir the thigh), the m. semitendinosus (the spine of the ischium laterad over the hip
joint to insert on the greater trochanter.
middle muscle of the caudal group),
and the m. semimembranosus (the The superficial gluteal muscle
medial muscle of this group). The divisions (m. gluteus superficialis) in species other
between these muscles can be seen as than ruminants extends from the sacral
vertical grooves in lean, muscular animals. vertebral spines to the third trochanter
In the horse, the m. biceps femoris and just distal to the greater trochanter. The
m. semitendinosus extend dorsad over the m. tensor fasciae latae extends from the
rump to attach to the sacral and caudal tuber coxae to the lateral femoral fascia,
(coccygeal) vertebral spines (the so‐called which attaches to the patella. In addition to
“vertebral heads” of these muscles). In abducting the hip joint, this muscle flexes
most other animals, the hamstring the hip joint and extends the stifle.
muscles originate almost exclusively from
the tuber ischiadicum. In ruminants, the Adductors and Rotators of the Hip.
m. biceps femoris is blended with the Adductors of the hip pull the limb toward
superficial gluteal muscle and is therefore the median plane. They are all on the
called the m. gluteobiceps. This combined medial aspect of the thigh, extending from
muscle is a powerful extensor of the hip, the pelvis to either the femur or the tibia.
stifle, and hock. The m. gracilis is the most medial muscle
The middle gluteal muscle (m. gluteus extending from the symphysis of the pelvis
medius) is another strong extensor of the to the tibia.
hip. It originates from the wing of the ilium The m. pectineus, a small spindle‐shaped
and inserts on the greater trochanter of the muscle deep to the m. gracilis, is both an
femur, a lever projecting above the hip. adductor and, owing to its somewhat cranial
position, a flexor of the hip.
Flexors of the Hip. Flexors of the hip are The m. adductor is the largest muscle
found cranial to the femur. The most on the medial side of the thigh. It extends
important are the m. iliacus and m. psoas from the ventral aspect of the pelvis to the
major, which insert on the lesser trochanter medial side of the femur and tibia. It is a
on the medial side of the femur. Owing to strong adductor but may also help to
the blending of the muscle bellies and extend the hip.
insertions, these muscles are often referred The m. quadratus femoris is an adductor
to collectively as the iliopsoas muscle. The of the thigh. Several other small muscles in
m. iliacus originates from the ventral this deep layer of hip musculature extend­
surface of the wing of the ilium. The m. ing from the area of the obturator foramen
psoas major originates from the ventral to the proximal femur are outward rotators
surfaces of the lumbar transverse processes. of the thigh. They include the internal and
The m. sartorius is a thin, straplike external obturator muscles (mm. obtura-
muscle that extends from the tuber coxae torius internus et externus), and the
to the tibia, diagonally crossing the medial mm. gemelli. Ruminants lack the internal
surface of the thigh. The m. rectus femoris obturator muscle.
(one head of the m. quadriceps femoris)
and the m. tensor fasciae latae also flex
the hip and are also described as extensors Muscles Acting on the Stifle
of the stifle.
Abductors of the Hip. Abductors of The stifle functions essentially as a hinge
the hip extend laterally over the hip joint joint, so the muscles acting on it are either
so as to move the limb away from the extensors or flexors.