Page 97 - Adams and Stashak's Lameness in Horses, 7th Edition

Functional Anatomy of the Equine Musculoskeletal System 63

a series of sacroiliac ligaments that contribute markedly nuchalis cranialis and the bursa subligamentosa supraspi­
to the overall stability of the joint and probably act to nalis, respectively. A third bursa (bursa subligamentosa
VetBooks.ir limbs. These ligaments can be summarized as the ventral nuchal ligament and the spine of the axis. 13,16
nuchalis caudalis) is inconsistently found between the
transfer most of the weight of the trunk to the pelvic
sacroiliac ligament, dorsal sacroiliac ligament, and inter­
osseous ligament. Muscles of the Trunk and Neck
The ventral sacroiliac ligament surrounds the joint
and fills the space between the ilium and the ventral Muscles of the torso (neck, trunk, and tail) may be
aspect of the wing of the sacrum. The dorsal sacroiliac roughly divided into those dorsal to the transverse pro­
ligament presents two distinct portions. One (dorsal or cesses (epaxial muscles) and those ventral to the trans­
short part) arises from tuber sacrale and inserts on the verse processes (hypaxial muscles). The dorsal branches
spinous processes of the sacral vertebrae. The other (lat­ of the spinal nerves innervate the epaxial muscles while
eral or long part) arises from tuber sacrale and the caudal hypaxial muscles receive their innervation from the ven­
edge of the ilial wing and inserts along the lateral aspect tral branches.
of the sacrum. From here it blends ventrad into the broad The epaxial muscles are extensors of the vertebral
sacrosciatic ligament that fills the space between the pel­ column and are themselves divided into three parallel
vis and sacrum. The interosseous ligament (interosseous bundles of fascicles: from lateral to medial these are the
sacroiliac l.) consists of strong, vertically oriented fibers iliocostalis system, the longissimus system, and the
between the ventral part of the wing of the ilium and the transversospinalis system (Figure 1.55). The iliocostalis
dorsal aspect of the wing of the sacrum. system (named for its attachments to the ilium and ribs)
does not extend into the neck. The others continue into
the cervical region and are associated with additional
Ligamentum Nuchae
distinct muscles. Of these, the splenius muscle is most
The topline of the neck is in part determined by the superficial (Figure 1.56). The splenius possesses capital
presence of the ligamentum nuchae (nuchal ligament), and cervical parts. Both arise from the third, fourth, and
which in horses extends from its cranial attachments on fifth thoracic spines and from the funicular part of the
the external occipital protuberance to the spinous pro­ nuchal ligament, and they insert on the nuchal crest of
cess of the third or fourth thoracic vertebra. Both parts the skull, the wing of the atlas, and the transverse pro­
of the nuchal ligament (funicular and laminar) are cesses of the third, fourth, and fifth cervical vertebrae.
paired. The rope‐like funicular part is connected to The splenius extends the neck and elevates the head, and
sheets that compose the laminar portions. These midline it is largely the rhythmic contraction of this powerful
elastic sheets arise from the second through fifth cervical muscle that creates the thrusting movements of the neck
vertebrae and insert on the spines of the second and third during the gallop. 27
24
thoracic vertebrae. Bursae are consistently found Deep to the splenius are a number of shorter muscles
between the funicular part of the nuchal ligament and extending from the cervical vertebrae to the skull; these
the atlas and between the nuchal ligament and the sec­ “specific activators of the head” are important in giving
ond thoracic spine. These are the bursa subligamentosa the head and neck its considerable range of motion.

M. complexus
(part of transversospinalis system)
M. spinalis
(part of transversospinalis system)
M. longissimus Tuber coxae
M. iliocostalis

M. sternomandibularis

Figure 1.55. Deep muscles of trunk.