SPECIAL MYOLOGY
MUSCLES OF THE BACK
There are very many muscles in the back, the bulk of them being formed by autochthonous muscles that originate from the dorsal parts of the trunk myotomes. They are covered by muscles which are displaced to the back from the head (visceral muscles) and upper limbs (truncopetal muscles). As a result the muscles of the back are arranged in two layers, the superficial and the deep layers. A. Superficial muscles. 1. Muscles attached to the shoulder girdle and upper arm: (a) the trapezius muscle, which is of branchial origin, moved to the trunk from the head and is therefore innervated by the eleventh cranial nerve (n. accessorius); (b) the latissimus muscle of the back, a truncopetal muscle, moved to the back from the head and is therefore supplied with nerves from the brachial plexus; (c) the levator muscle of scapula and the rhomboid muscle are truncofugal muscles which moved from the trunk to the shoulder girdle and are innervated by the short branches of the brachial plexus. 2. Muscles attached to the ribs: the superior and inferior posterior serratus muscles; both are derivatives of the ventral trunk musculature which have been displaced to the back. They are innervated by the anterior branches of the spinal nerves (nn. intercostales). B. Deep muscles. Like the skeleton, the muscles of the axial skeleton are the first to arise in the process of phylogenesis. In man's ontogenesis they, consequently, appear first and lie deeper, preserving the primitive metameric structure. According to origin, they are grouped as follows: Autochthonous muscles, derived from the dorsal parts of the myotomes and innervated, therefore, by the dorsal branches of the spinal nerves. Deep muscles of ventral origin, innervated, therefore, by anterior branches of the spinal nerves. These are the anterior intertransverse muscles of the neck, the lateral intertransverse muscles of the loins, and the levatores costarum muscles.
There are very many muscles in the back, the bulk of them being formed by autochthonous muscles that originate from the dorsal parts of the trunk myotomes. They are covered by muscles which are displaced to the back from the head (visceral muscles) and upper limbs (truncopetal muscles). As a result the muscles of the back are arranged in two layers, the superficial and the deep layers. A. Superficial muscles. 1. Muscles attached to the shoulder girdle and upper arm: (a) the trapezius muscle, which is of branchial origin, moved to the trunk from the head and is therefore innervated by the eleventh cranial nerve (n. accessorius); (b) the latissimus muscle of the back, a truncopetal muscle, moved to the back from the head and is therefore supplied with nerves from the brachial plexus; (c) the levator muscle of scapula and the rhomboid muscle are truncofugal muscles which moved from the trunk to the shoulder girdle and are innervated by the short branches of the brachial plexus. 2. Muscles attached to the ribs: the superior and inferior posterior serratus muscles; both are derivatives of the ventral trunk musculature which have been displaced to the back. They are innervated by the anterior branches of the spinal nerves (nn. intercostales). B. Deep muscles. Like the skeleton, the muscles of the axial skeleton are the first to arise in the process of phylogenesis. In man's ontogenesis they, consequently, appear first and lie deeper, preserving the primitive metameric structure. According to origin, they are grouped as follows: Autochthonous muscles, derived from the dorsal parts of the myotomes and innervated, therefore, by the dorsal branches of the spinal nerves. Deep muscles of ventral origin, innervated, therefore, by anterior branches of the spinal nerves. These are the anterior intertransverse muscles of the neck, the lateral intertransverse muscles of the loins, and the levatores costarum muscles.