152 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 241. — The deeper layers of the long muscles of the back. 



On the left side the sacrospinalis has been partly removed and the semispinalis has been cut and reflected. 



Fig. 242. — The cervical portion of the deeper layers of the muscles of the back, seen from the side. 

 The trapezius and splenii have been removed. 



undergone but slight changes. They are arranged in three layers, each of which is described as 

 a special muscle, although they are not separated by fascia?, but are distinguishable from each 

 other chiefly by the length of their fasciculi. The semispinali s, the most superficial layer, has the 

 longest and consequently the most slanting fibers, which bridge over from four to six spinous 

 processes; the inulti fidus. the middle layer, has fasciculi which pass over two or three vertebral 

 spines; and the r ota tores , forming the deepest layer, either extend over only one spinous process 

 { rotator es longi) or pass to the next succeeding vertebra {rotator es brevi). With the exception of 

 the semispinalis capitis, all of the fibers of the transversospinalis end at the spinous process of the 

 axis. The semispinalis is absent in the lumbar region, and the rotatores are situated chiefly in 

 the thoracic region. 



The se mispin alis (Figs. 239, 241, and 242) consists of the semispinalis dorsi, semispinalis 

 cervicis, and semispinalis capitis. 



'The semispinalis dgj^i (Figs. 239 and 241) and cervicis (Fig. 241) are directly continuous 

 without demarcation, the lowermost fibers arising from the transverse processes of the lower 

 thoracic vertebrae, and the uppermost fasciculi terminating at the spinous process of the axis. 

 The muscle is stronger and more fleshy in the neck' than it is in the back. The fibers of the 

 semispinalis dorsi are intermingled with numerous tendinous fasciculi and are also partly con- 

 nected with the spinalis dorsi. The muscle is completely covered by the longissimus dorsi and 

 the semispinalis capitis. 



The semispinalis c apiti s (Figs. 239, 241, and 242) is aflat but rather thick muscle and is the 

 strongest muscle of the neck. As a rule, it consists of two portions which are separated below but 

 adherent above at their insertion — a stronger external or semispinal portion and a weaker internal 

 or spinal portion. The semispinal segment, sometimes termed the com plexus, arises by numerous 

 short tendinous slips from the transverse processes of the third cervical to the fifth or sixth thoracic 

 vertebra?, while the spinal segment arises from the spinous processes of the lower cervical and of 

 the upper thoracic vertebrae (the spinalis capitis). This latter portion is characterized by a tendin- 

 ous inscription, and hence is sometimes termed the biventer cervicis, and sometimes, when the 

 spinalis capitis is absent, its origin extends to the transverse processes of the second to the sixth 

 cervical vertebrae. The external portion of the muscle also usually possesses a broad tendinous 

 inscription which is situated above the middle tendon of the biventer. Both portions of the 

 muscle unite and pass to the nuchal surface of the occipital bone, where they insert between the 

 superior and inferior nuchal lines. 



The multifjdu s (Figs. 241 and 242) consists of the multifidus himborum . dorsi, and cervicis , 

 but these segments cannot be clearly demarcated from each other. It commences below at the 

 posterior surface of the sacrum and terminates above at the spinous process of the epistropheus 

 (axis). It is strongest in the lumbar -region, where it lies directly beneath the longissimus; it is 

 weakest in the thoracic region, where it is covered by the semispinalis dorsi; and in the cervical 



