Spinal Muscles The spinal muscles are a complicated group of muscles that pass along the back of the animal from the pelvis to the middle of the neck. Each muscle consists of numerous overlapping bundles that continuously originate and insert along the spine. They lie on either side of the upper surface of the vertebral column, separated by the upright spines. This powerful muscle group consists of four units: the longissimus, the iliocostalis, the spinalis & semispinalis, and the multifidus, all of which may be divided into regional components (cervicis, thoracis & lumborum).The longissimus, iliocostalis and spinalis comprise the. | 52 INDIVIDUAL MUSCLES TRUNK Spinal Muscles The spinal muscles are a complicated group of muscles that pass along the back of the animal from the pelvis to the middle of the neck. Each muscle consists of numerous overlapping bundles that continuously originate and insert along the spine. They lie on either side of the upper surface ofthe vertebral column separated by the upright spines. This powerful muscle group consists of four units the longissimus the iliocostalis the spinalis semispinalis and the multifidus all of which may be divided into regional components cervicis thoracis lumborum . The longissimus iliocostalis and spinalis comprise the erector spinae sacrospinalis . The longissimus capitis to the head and longissimus atlantis to the first neck vertebra are described with the neck muscles. Action They primarily extend the vertebral column. Their contraction will also fix the spine into a rigid column. A muscle contracting on one side only will bend the spine toward that side. Some units also pull the ribs rearward which assists in breathing. HORSE AND OX Longissimus cervicis thoracis lumborum Origin Deep surface ofthe front ofthe pelvis from its inner to its outer expansions and the upper bony projections ofthe thoracic and lumbar vertebrae and front half of the sacrum. Insertion Sides ofthe thoracic and lumbar vertebrae the upper ends of all the ribs except the first and the sides and tops ofthe last four neck vertebrae fourth through the seventh . Structure The longissimus is the longest and largest muscle in the body. The thick lumbar portion is called the common mass. A depression in its upper surface just to the front ofthe pelvis gives origin to the gluteus medius muscle. This depression in the ox is smaller and doesn t advance as far forward as in the horse. At the middle ofthe trunk the longissimus divides into upper and lower portions both of which insert into the last four neck vertebrae. The upper portion the spinalis semispinalis inserts into .
