352 MUSCLES AND FASCIAE. 



Relations. By its superficial surface, with the Latissimus Dorsi, with the 

 aponeurosis of which its own aponeurotic origin is inseparably blended. By 

 its deep surface, with the lumbar fascia, the Erector Spina?, ribs, and Intercostal 

 muscles. Its upper margin is- continuous with the vertebral aponeurosis. 



The vertebral aponeurosis is a thin aponeurotic lamina, extending along the 

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

 Erector Spinae, and separating it from those muscles which connect the spine 

 to the upper extremity. It consists 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 vertebrae ; externally, to the angles of the ribs ; 

 and below, to the upper border of the Inferior Serratus and tendon of the Latis- 

 simus Dorsi ; above, it passes beneath the Splenius, and blends with the deep 

 fascia of the neck. 



Now detach the Serratus Posticus Superior from its origin, and turn it outwards, 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 

 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 

 dorsal vertebrae, and from the supraspinous ligament. From this origin, the 

 fleshy fibres proceed obliquely upwards and outwards, 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 beneath the superior curved line. 



The Splenius Colli is inserted, by tendinous fasciculi, into the posterior tuber- 

 cles of the transverse processes of the three or four upper cervical vertebra. 



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 surface, with the Trapezius, from which it is 

 separated below by the Ehomboidei and the Serratus Posticus Superior. It is 

 covered at its insertion by the Sterno-rnastoid. By its deep surface, with the 

 Spinalis Dorsi, Longissimus Dorsi, Sernispinalis Colli, Complexus, Trachelo- 

 mastoid, and Transversalis Colli. 



Nerves. The Splenius and Superior Serratus are supplied from the external 

 posterior branches of the cervical nerves ; the Inferior Serratus, from the ex- 

 ternal branches of the dorsal nerves. 



Actions. The Serrati .are respiratory muscles acting in antagonism to each 

 other. The Serratus Posticus Superior elevates the ribs ; it is, therefore, an 

 inspiratory muscle ; while the Serratus Inferior draws the lower ribs down- 

 wards, and is a muscle of expiration. This muscle is also probably a tensor 

 of the vertebral aponeurosis. The Splenii muscles of the two sides, acting 

 together, draw the head directly backwards, 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 sup- 

 porting the head in the erect position. 



FOURTH LAYER. 



Sacral and Lumbar Regions. Cervical Region. 



Erector Spinae. Cervicalis Ascendens. 



Transversalis Colli. 



Dorsal Region. Trachelo-mastoid. 



Sacro-lumbalis. Complexus. 



Musculus Accessorius ad Sacro-lumbalem. Biventer Cervicis. 



Longissimus Dorsi. Spinalis Colli. 

 Spinalis Dorsi. 



