OF THE BACK. 273 



outwards, it is inserted into the margin of the triangular smooth surface at the 

 root of the spine of the scapula. This small muscle is usually separated from the 

 Rhomboideus major by a slight cellular interval. 



The Ehomboideus Major is situated immediately below the preceding, the adja 

 cent margins of the two being occasionally united. It arises by tendinous fibres 

 from the spinous processes of the four or five upper dorsal vertebrae and the supra- 

 spinous ligament, and is inserted into a narrow, tendinous arch, attached, above, to 

 the triangular surface near the spine ; below, to the inferior angle, the arch being 

 connected to the border of the scapula by a thin membrane. When the arch 

 extends, as it occasionally does, but a short distance, the muscular fibres are 

 inserted into the scapula itself. 



Relations. By their superficial surface, with the integument, and Trapezius ; 

 the Rhomboideus major, with the Latissimus dorsi. By their deep surface, with 

 the Serratus posticus superior, posterior scapular artery, part of the Erector spinae, 

 the Intercostal muscles and ribs. 



Nerves. These muscles are supplied by branches from the fifth cervical nerve, 

 and additional filaments from the deep branches of the cervical plexus are distrib- 

 uted to the Levator anguli scapulas. 



Actions. The movements effected by the preceding muscles are numerous, as 

 may be conceived from their extensive attachment. If the head is fixed, the upper 

 part of the Trapezius will elevate the point of the shoulder, as in supporting 

 weights ; when the middle and lower fibres are brought into action, partml rotation 

 of the scapula upon the side of the chest is produced. If the shoulders are fixed, 

 both Trapezii acting together will draw the head directly backwards, or, if only 

 one acts, the head is drawn to the corresponding side. 



The Latissimus dorsi, when it acts upon the humerus, draws it backwards and 

 downwards, and at the same time rotates it inwards. If the arm is fixed, the 

 muscle may act in various ways upon the trunk ; thus, it may raise the lower ribs 

 and assist in forcible inspiration, or, if both arms are fixed, the two muscles may 

 conspire with the Abdominal and great Pectoral muscles in drawing the whole 

 trunk forwards, as in climbing or walking on crutches. 



The Levator anguli scapulae raises the superior angle of the scapula after it has 

 been depressed by the lower fibres of the Trapezius, whilst the Rhomboid muscles 

 carry the inferior angle backwards and upwards, thus producing a slight rotation 

 of the scapula upon the side of the chest. If the shoulder be fixed, the Levator 

 scapulae may incline the neck to the corresponding side. The Rhomboid muscles, 

 acting together with the middle and inferior fibres of the Trapezius, will draw the 

 scapula directly backwards towards the spine. 



THIRD LAYER. 



Serratus Posticus Superior. Serratus Posticus Inferior. 



01- ( Splenius Capitis. 



oplemus { 01 n ir 



( Splenius Com. 



Dissection. The third layer of muscles is brought into view by the entire removal of the pre. 

 ceding, together with the Latissimus dorsi. To effect this, the Levator anguli scapulae and 

 Rhomboid muscles should be detached near their insertion, and reflected upwards, thus exposing 

 the Serratus posticus superior ; the Latissimus dorsi should then be divided in the middle by a 

 vertical incision carried from its upper to its lower part, and the two halves of the muscle reflected. 



The Serratus Posticus Superior is a thin, flat muscle, quadrilateral in form, 

 situated at the upper and back part of the thorax. It arises by a thin and broad 

 aponeurosis, from the ligamentum nuchae and from the spinous processes of the 

 last cervical and two or three upper dorsal vertebrae. Inclining downwards and 

 outwards, it becomes muscular, and is inserted, by four fleshy digitations, into 

 the upper borders of the second, third, fourth, and fifth ribs, a little beyond their 

 angles. 



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