528 DISSECTION OF THE BACK. 



Relations of Relations of the erector spince. The erector spinae is concealed 



fumbaraud 1)V tne muscles of the layers already examined. It lies over the 



dorsal semispinalis and nmltifidus spinae muscles, portions of the ribs and 



external intercostal muscles, and the levatores costarum. In the 

 loins it is contained in the aponeurotic sheath of the fascia lum- 

 borum, and in the thoracic region a similar sheath is formed for 

 the muscle by the vertebral aponeurosis with the ribs and dorsal 

 vertebrae. The tendon of origin is united over the sacrum with 

 the posterior layer of the fascia lumborum ; and from its outer 

 border in this part some fibres of the glutens maximus arise. 



and in neck. The prolongations of the muscle in the neck lie between the 

 splenius and levator anguli scapulas on the outer side and the corn- 

 plexus on the inner side, the trachelo-mastoid being next to the 

 complexus. The cervicalis ascendens is attached to the transverse 

 processes in a line with the splenius colli, and immediately behind 

 the middle and posterior scalene muscles. 



Use of both Action of erector spince. These powerful muscles draw backwards 

 ors ' or extend the spine, and come into play in bringing the column 

 into, and in maintaining the erect position. The parts inserted into 

 the dorsal vertebrae will be to some extent inspiratory muscles, 

 since the dilatation of the thorax is aided by extension of the verte- 

 bral column ; but the slips inserted into the ribs will draw down- 

 wards these bones, and may thus act in forced expiration. The 



of one muscle of one side acting alone will incline the spine laterally. The 



orations* cervical prolongations have a similar action upon the neck and head. 



in neck. FIFTH LAYER OF MUSCLES. Iii this layer are included the 



com pl exus > tne semispinalis, and the multifidus spinae ; and most of 

 the vessels and nerves of the back are to be learnt with this layer 

 of muscles. 



Dissection of Dissection. To display the complexus (fig. 191) it will only 

 ais> be necessary to turn outwards the cervical prolongations of the 

 erector spinae muscle, and follow down the slips of origin to the 

 dorsal transverse processes. The semispinalis and multifidus are 

 now partly seen below the complexus, lying between the erector 

 spinse and the spines of the vertebrae. 



Complexus: The COMPLEXUS (fig. 191, D) is internal to the prolongations 

 from the longissimus dorsi, and converges towards its fellow of the 

 opposite side at the occipital bone. Narrow at its lower end, the 



origin; muscle arises by tendinous slips from the transverse processes of 

 the upper six dorsal and seventh cervical vertebrae, and from the 

 articular processes of the succeeding cervical vertebrae as high as 

 the third : it is also joined in most cases by one or two slips from 

 the lowest cervical or upper dorsal spines. The fleshy fibres pass 



insertion ; upwards to be inserted into an impression between the curved lines 

 of the occipital bone, which reaches outwards nearly two inches 

 from the external occipital crest. 



tendinous The inner part of the complexus, having two fleshy bellies with 



sections ; an intervening tendon, is often described separately as the biventer 

 cervicis. Another tendinous intersection crosses the cutaneous 

 surface of the muscle near the upper end. 



