Page 165 - Anatomy and Physiology of Farm Animals, 8th Edition

150 / Anatomy and Physiology of Farm Animals

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Figure 7-18. Nuchal ligament of the horse. Red, funicular part; blue, laminar part.

aid to the muscles that extend and support Abdominal Muscles
the head and neck. It has a rope‐like funic-
ular portion attached to the skull and a The muscles that form the bulk of the
sheet‐like laminar portion that attaches abdominal wall support the organs of
to the dorsal aspects of C2 through C7. digestion and many of the reproductive
The pig lacks a nuchal ligament. organs, particularly the gravid (pregnant)
uterus. The abdominal muscles also flex
the vertebral column. If contracting on
Flexors of the Vertebral Column one side only, they flex it laterally or even
twist the vertebral column. Through their
Muscles ventral to the transverse processes ability to compress the abdominal con­
of the vertebrae are the hypaxial muscles. tents, these muscles are important in emp­
They flex the trunk, neck, and head. In the tying the contents of the digestive tract
neck region these include the m. sternoce- (defecation), urinary tract (urination, also
phalicus, which extends from the sternum called micturition), and female reproduc­
to the mandible in the horse and to the tive tract at birthing (parturition). The
mandible and mastoid process of the skull abdominal muscles are also used in regur­
in ruminants. In addition, the m. sterno- gitation and vomiting and serve as strong
thyroideus, m. sternohyoideus, m. longus muscles for forced exhalation of air from
colli, and m. longus capitis are flexors of the lungs, as seen during coughing or
the neck. sneezing.
Caudal to the neck, flexion of the vertebral The abdominal muscles are arranged in
column is largely accomplished by ventral layers much like plywood, with the muscle
muscles that are part of the abdominal wall fibers running in different directions. Most
(see below). In the lumbar region, long, of these muscles have broad aponeurotic
thick muscles that attach to the ventral insertions that meet at the midventral line
aspect of the vertebral bodies and/or their known as the linea alba (white line).
transverse processes can produce strong The external abdominal oblique m.
flexion. These include the m. psoas major, (m. obliquus externus abdominis) is the
m. psoas minor, and the m. quadratus most superficial. The fibers of this muscle
lumborum. In beef cattle, these muscles run obliquely ventrad and caudad. Its origin
are what constitute the tenderloin and a is from the last few ribs and thoracolumbar
portion of the T‐bone steak. (lumbodorsal) fascia over the back and