172 



MUSCLES OF THE TRUNK. 



inferior thyroid artery. By its posterior surface it rests upon the 

 cervical and upper dorsal vertebrae. 



Actions. The rectus anticus major and minor preserve the equi- 

 librium of the head upon the atlas ; and acting conjointly with the 

 longus colli, they flex and rotate the head and the cervical portion 

 of the vertebral column. The scaleni muscles, taking their fixed 

 point from below, are flexors of the vertebral column ; and, from 

 above, elevators of the ribs, and therefore inspiratory muscles. 



Eight/i Group. Muscles of the Larynx. 



These muscles are described with the anatomy of the larynx, in 

 Chapter X. 



MUSCLES OF THE TRUNK. 



The muscles of the trunk may be subdivided into four natural 

 groups ; viz. 



1. Muscles of the back. 



2. Muscles of the thorax. 



3. Muscles of the abdomen. 



4. Muscles of the perineum. 



1. Muscles of the back. The region of the back, in consequence of 

 its extent, is common to the neck, the upper' extremities, and the 

 abdomen. The muscles of which it is composed are numerous, 

 and may be arranged into six layers. 



First Layer. 

 Trapezius, 

 Latissimus dorsi. 



Second Layer. 

 Levator anguli scapulae, 

 Rhomboideus minor, 

 Rhomboideus major. 



Third Layer. 



Serratus posticus superior, 

 Serratus posticus inferior, 

 Splenius capitis, 

 Splenius colli. 



Fourth Layer. 



(Dorsal Group). 

 Sacro lumbalis, 

 Longissimus dorsi, 

 Spinalis dorsi. 



(Cervical Group.) 

 Cervicalis ascendens, 



Transversalis colli, 



Trachelo-mastoideus, 



Complexus. 



Fifth, Layer. 



(Dorsal Group.) 

 Semi-spinalis dorsi, 

 Semi-spinalis colli. 



(Cervical Group.) 

 Rectus posticus major, 

 Rectus posticus minor, 

 Rectus lateralis, 

 Obliquus inferior, 

 Obliquus superior. 



Sixth Layer. 

 Multifidus spinae, 

 Levatores costarum, 

 Supra-spinales, 

 Inter-spinales, 

 Inter-transversales. 



