240 DORSAL MUSCLES OF THE TEUNK. 



thence obliquely upwards and backwards, increasing somewhat as it ascends, 

 and is inserted into a groove situated externally to the inferior curved line 

 of the occipital bone. 



The two oblique muscles, with the rectus major, form the sides of a small triangular 

 space, in the area of which the posterior primary branch of the sub-occipital nerve 

 and the vertebral artery will be found. 



ACTIONS. The transverso-spinales muscles, including the complexus, are essentially 

 extensors of the head and vertebral column ; and the movements produced by them 

 vary according as the muscles of one side or both are in action, in a manner similar 

 to that already pointed out in regard to the erector muscles. 



The interspinales and intertransversales muscles approximate the vertebras between 

 which they pass, and thus may act as extensors and lateral flexors respectively of the 

 portion of the vertebral column in which they are situated. 



Of the four muscles last described, two the rectus minor and superior oblique 

 act principally by drawing the head backwards, that being the chief movement 

 allowed between the atlas and occipital bone ; while the principal action of the rectus 

 posticus major and the inferior oblique, when acting on one side, is to rotate the atla.s 

 and skull upon the axis. 



DORSAL AND LUMBAR FASCIA. Under the name of lumbar fascia or 

 aponeurosis it has been customary to describe three layers of strong fibrous 

 substance sheathing the erector spinse and quadratus lumboruni muscles. 

 The deeper parts of this structure, to which by some the name of lumbar 

 fascia is restricted, will be described along with the abdominal muscles, with 

 which they are chiefly connected. The superficial or posterior layer is that 

 through which the latissimus dorsi and serratus posticus inferior are attached 

 to the spines of the dorsal, lumbar and sacral vertebrae and to the crest of 

 the ilium. This layer, which is of considerable strength, extends outwards 

 beyond the origin of the latissimus and serratus inferior, and being closely 

 united with the middle layer, binds down firmly the erectores spinse 

 muscles : it is by some described as the lower part of the vertebral aponeu- 

 rosis, with which it is continuous, by others it has been named the 

 aponeurosis of the latissimus dorsi. 



The vertebral aponeurosis, strictly so called, is situated on the same plane 

 as the serratus posticus inferior, and consists of a thin lamella which sepa- 

 rates the muscles belonging to the shoulder and arm from those which 

 support the spine and head. Its fibres are for the most part transverse ; 

 some however are longitudinal. Above, it passes beneath the superior 

 serratus ; below, it is connected with the tendons of the latissimus and 

 inferior serratus muscles, and in being stretched from the spinous processes 

 outwards across the vertebral groove, it helps to enclose the angular canal in 

 which are lodged the long extensor muscles. 



MUSCLES OP THE THORAX. 



The muscles of the thoracic wall are the intercostales, levatores costarum, 

 subcostales and triangularis sterni, and along with these the diaphragm inter- 

 vening between the thorax and abdomen may conveniently be grouped. 



The intercostal muscles consist of two thin layers of oblique short muscular 

 fibres filling up the inter-costal spaces : these layers are named respectively 

 the external and internal muscles. 



The external intercostal muscles are formed of muscular fibres, with some 

 tendinous fibres intermixed, directed obliquely downwards and forwards 

 from one rib to another. Their extent for the most part is from the 



