Page 98 - Adams and Stashak's Lameness in Horses, 7th Edition

64 Chapter 1

M. splenius
VetBooks.ir M. serratus ventralis

M. trapezius
M. latissimus dorsi

M. sternomandibularis

M. brachiocephalicus
M. omotransversarius

M. obliquus
externus abdominis
M. pectoralis ascendens

Figure 1.56. Superficial muscles of trunk. Cutaneous muscles have been removed.

Among those dorsal to the transverse processes are the In the ventral neck, the equine m. longus colli is par­
cranial and caudal parts of the obliquus capitis muscle. ticularly well developed relative to other domestic spe­
The cranial part bridges between the nuchal crest and cies. The cervical portion of this muscle arises from the
the cranial border of the wing of the atlas. The caudal transverse processes and bodies of the third through
part is a large, powerful rotator of the atlantoaxial joint. sixth cervical vertebrae in paired bundles that converge
It attaches to the cranial border of the wing of the atlas to an insertion on the preceding vertebral bodies, some­
and the vertebral arch of the axis. times bridging more than one intervertebral space. The
Deep to the oblique muscles are a series of straight most cranial attachment is on the ventral aspect of the
muscles that link the skull to the atlas and axis. The atlas. The thoracic portion of the longus colli arises on
major part of rectus capitis dorsalis attaches on the cau­ the lateral vertebral bodies of thoracic vertebrae one
dal aspect of the occipital bone and the spinous process through six, passing craniad to insert on the transverse
of the axis; its minor portion lies dorsal to the dorsal processes of cervical vertebrae six and seven.
atlanto‐occipital membrane, bridging between occipital The omohyoideus muscle is well developed in the
bone and the wing of the atlas. Rectus capitis ventralis horse. It arises from an aponeurosis in the fascia near
runs from the base of the skull to the ventral arch of the the shoulder joint. Its muscle belly is closely attached to
atlas. Rectus capitis lateralis attaches from the wing of the deep side of the brachiocephalicus until the neck’s
the atlas to the paracondylar process. These last two midpoint, where the omohyoideus becomes evident as a
muscles are relatively weak in the horse. distinct muscle as it passes craniad deep to the sternoce­
The longus capitis muscle bridges between the trans­ phalicus muscle. Near its insertion on the lingual pro­
verse processes of C2 through C4 or C5 and the ventral cess, it fuses with its partner from the contralateral side
skull. and with the sternohyoideus.
Activators of the head that are above the transverse The right and left sternomandibularis muscles of the
processes will extend the atlanto‐occipital and atlanto­ horse are fused on midline near their origin on the man­
axial joints; those ventral to the transverse processes ubrium. Near mid‐neck, the two halves separate, mov­
flex those joints. When acting unilaterally, all of these ing from their position ventral to the trachea to a more
muscles have the ability to turn the head laterally. lateral location. As the muscle approaches its insertion
The longissimus group is described as having lumbar, on the sternomandibular tuberosity on the ramus of the
thoracic, cervical, atlantal, and capital portions. It is most mandible, it narrows to a distinct tendon that is visible
robust in the lumbar region, where it gives a well‐condi­ in the cranial neck just caudal to the caudal border of
tioned horse’s back its typical rounded appearance. the mandible. The tendon of insertion is classically con­
Hypaxial muscles of the trunk (the psoas minor, sidered one side of Viborg’s triangle.
quadratus lumborum, and the four abdominal muscles
on each side) act to flex the vertebral column during the
gallop. Epaxial muscles extend the vertebral column. ACKNOWLEDGMENT
When they contract unilaterally, both hypaxial and
epaxial muscles create lateral movement of the trunk The authors thank Dr. Robert A. Kainer for his con­
and neck. tributions to this chapter in the previous edition.