OF THE BACK. 433 



The thin aponeurosis of origin is intimately blended with the tendon of origin of 

 the Latissimus dorsi muscle and with the lumbar fascia (posterior layer). 



Relations. By its snpern<-ial surface, Avith the Latissimus dorsi, with the 

 aponeurosis of which its own aponeurotic origin is inseparably blended ; by its 

 surface, the Erector spinoe, ribs, and Intercostal muscles. Its upper margin 

 is continuous with the vertebral aponeurosis. 



The }\'rt>'lrai apont'iiroxis is a thin, fibrous lamina extending along the whole 

 length of the back part of the thoracic region, serving to bind down the long 

 extensor muscles of the back which support the spine and head, and separate 

 them from those muscles which connect the spine to the upper extremity. It con- 

 sists of longitudinal and transverse fibres blended together, forming a thin lamella, 

 which is attached in the median line to the spinous processes of the dorsal vertebra; 

 externally, to the angles of the ribs ; and below, to the aponeurosis of the Serratus 

 posticus inferior and tendon of origin of the Latissimus dorsi, with both of which 

 it is continuous ; above, it passes beneath the Serratus posticus superior, and 

 blends with the deep fascia of the neck. 



The Lumbar fascia (Figs. 287 and 295) occupies the interval between the last 

 rib and crest of the ilium. It is attached internally to the spinous process of the . 

 lumbar and sacral vertebrae ; above, to the last rib and to the cartilage of the 

 eleventh rib ; below, to the posterior third of the crest of the ilium. The posterior 

 layer of this fascia blends with, and is practically the same thing as, the aponeu- 

 rosis of the Latissimus dorsi and Serratus posticus inferior. It gives attachment 

 to the Internal oblique muscle of the abdomen. The anterior or deep surface 

 gives off two layers : one lies between the Erector spinse and Quadratus lumborum, 

 and is attached to the tips of the transverse processes of the lumbar vertebrae 

 (posterior aponeurosis of the Transversalis muscle); the other lies on the anterior 

 or internal surface of the Quadratus lumborum, and is attached to the front part 

 of the same transverse processes (transversalis fascia). The upper portion of this 

 layer, which extends from the transverse process of the first lumbar vertebra to 

 the apex and lower border of the last rib, constitutes the ligamentum arcuatum 

 externum. Therefore these three layers of the lumbar fascia form two spaces : 

 between the posterior and middle layer is situated the Erector spinae and the 

 Multifidus spinse ; between the middle and anterior layers is situated the Quad- 

 ratus 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 is situated at the back of the neck and upper part of the dorsal 

 region. At its origin it is a single muscle, narrow, and pointed in form ; but it 

 soon becomes broader, and divides into two portions, which have separate inser- 

 tions. 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 dorsal vertebrae, 

 and from the supraspinous ligament. From this origin the fleshy fibres proceed 

 obliquely upward and outward, forming a broad flat muscle, which divides as it 

 ascends into two portions, the Splenius capitis and Splenius colli. 



The 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 is inserted, by tendinous fasciculi, into the posterior tubercles 

 of the transverse processes of the two or three upper cervical vertebrae. 



The Splenius is separated from its fellow of the opposite side by a triangular 

 interval, in which is seen the Complexus. 



Relations. By its superficial s;trface, with the Trapezius, from which it is 

 separated below by the Rhomboidei and the Serratus posticus superior. It is 

 covered at its insertion by the Sterno-mastoid, and at the lower and back part of 

 the neck by the Levator anguli scapulae : by its deep surface, with the Spinalis 

 dorsi, Longissimus dorsi, Semispinalis colli, Complexus, Trachelo-mastoid, and 

 Transversalis colli. 



28 



