410 THE MUSCLES AND FASCIA 



extremity. It consists of longitudinal and transverse fibres blended together, 

 forming a thin lamella, which is attached, in the median line, to the spinous pro- 

 cesses of the thoracic vertebrae; externally, to the angles of the ribs; and is contin- 

 uous with the intercostal fascia below. It is continuous below with the aponeurosis 

 of the Serratus posticus inferior and a portion of the lumbar fascia, which gives 

 origin to the Latissimus dorsi; above, it passes beneath the Serratus posticus 

 superior and the Splenius, and blends with the deep fascia of the neck. 



The lumbar fascia or aponeurosis (Figs. 312 and 327), which may be regarded 

 as the posterior aponeurosis of the Transversalis abdominis muscle, consists of 

 three laminae, which are attached as follows: The dorsal layer, to the spines of 

 the lumbar and sacral vertebras and their supraspinous ligaments; the middle 

 layer, to the tips of the transverse processes of the lumbar vertebrae and their 

 intertransverse ligaments; the ventral layer, to the roots of the lumbar transverse 

 processes. The dorsal layer is continued above as the vertebral aponeurosis, 

 while inferiorly it is fixed to the outer lift of the iliac crest. With this layer are 

 blended the aponeurotic origin of the Serratus posticus inferior and part of that 

 of the Latissimus dorsi. The middle layer is attached above to the last rib, and 

 below to the iliac crest; the ventral layer is fixed below to the iliolumbar ligament 

 and iliac crest; while above it is thickened to form the external arcuate ligament 

 of the Diaphragm, and stretches from the tip of the last rib to the transverse pro- 

 cess of the first or second lumbar vertebra. These three layers, together with 

 the vertebral column, enclose two spaces, the posterior of which is occupied by 

 the Erector spinae muscle, and the anterior by the Quadratus lumborum. 



Now detach the Serratus posticus superior from its origin, and turn it outward, when the 

 Splenius muscle will be brought into view. 



The Splenius muscle mass (Fig. 312) is situated at the back of the neck and 

 upper part of the thoracic region. At its origin it is a single muscle, which soon 

 after its origin becomes broad, and divides into two portions, which have separate 

 insertions. It arises, by tendinous fibres, from the lower half of the ligamentum 

 nuchae, from the spinous processes of the last cervical and of the six upper tho- 

 racic vertebrae, and from the supraspinous ligament. From this origin the fleshy 

 fibres proceed obliquely upward and outward, forming a broad, flat muscle sheet, 

 which divides as it ascends into two portions, the Splenius capitis and Splenius colli. 



The Splenius capitis (m. splenius capitis) is inserted into the mastoid process of 

 the temporal bone, and into the rough surface on the occipital bone, just beneath 

 the superior curved line. 



The Splenius colli (m. splenius cervicis] is inserted, by tendinous fasciculi, into the 

 posterior tubercles of the transverse processes of the two or three upper cervical 

 vertebrae. 



The Splenius muscles are separated from their fellows of the opposite side by a 

 triangular interval, in which is seen the Complexus. 



Nerves. The Splenius capitis and colli muscles are supplied from the external branches of 

 the posterior primary divisions of the middle and lower cervical nerves; the Serratus posticus 

 superior is supplied by the external branches of the upper three or four intercostal nerves; the 

 Serratus posticus inferior by branches of the ninth, tenth, and eleventh intercostal nerves. 



Actions. The Serrati are respiratory muscles. The Serratus posticus superior elevates the 

 ribs; it is therefore an inspiratory muscle; while the Serratus inferior draws the lower ribs down- 

 ward and backward, and thus elongates the thorax. It also fixes the lower ribs, thus aiding the 

 downward action of the Diaphragm and resisting the tendency which it has to draw the lower 

 ribs upward and forward. It must therefore be regarded as a muscle of inspiration. This 

 muscle is also probably a tensor of the vertebral aponeurosis. The Splenii muscles of the two 

 sides, acting together, draw the head directly backward, assisting the Trapezius and Com- 

 plexus; acting separately, they draw the head to one or the other side, and slightly rotate it, turning 

 the face to the same side. They also assist in supporting the head in the erect position. 



