144 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



7. The muscles of the upper back and shoulder and back of the neck. 



(Fig. 42.) 

 Rabbit: 



a) Latissimus dorsi. Turn the animal on one side, so that the side on which 

 the muscles have already been dissected will be uppermost. The large flat 

 muscle extending obliquely from the middle of the back to the fore limb is the 

 latissimus dorsi. Origin, lumbodorsal fascia and posterior ribs; insertion, on 

 the crest on the medial side of the humerus, the insertion covered by the chest 

 muscles; action, draws the arm caudad and dorsad. 



b) Anterior and posterior trapezius. These two muscles are the flat, thin 

 muscles covering the upper back and back of the neck anterior to the latissimus 

 dorsi. The posterior trapezius originates from the lumbodorsal fascia and the 

 neural spines of the thoracic vertebrae, and is inserted on the spine of the scapula. 

 Action, draws the scapula dorsally. The anterior trapezius originates on the 

 external occipital protuberance of the skull and ligament in the mid-dorsal line 

 and is inserted on the metacromion process (which is very long in the rabbit) and 

 nearby muscles and fascia; action, draws the scapula and limb upward and for- 

 ward. The space between the two trapezius muscles is filled by a stout 

 fascia. 



c) Levator scapulae ventralis. This long slender muscle runs along the ventral 

 border of the anterior trapezius near its insertion, then diverges to its origin 

 from the ventral surface of the skull at the suture between occipital and basisphe- 

 noid; insertion, metacromion process in common with the anterior trapezius; 

 action, pulls the scapula anteriorly. 



d) Rhomboideus. Cut across the middle of the bellies of the two trapezius 

 muscles and the latissimus dorsi. The large thick muscle extending from the 

 vertebral border of the scapula to the mid-dorsal line is the rhomboideus. 

 Origin, mid-dorsal ligament of the neck and succeeding neural spines; insertion, 

 vertebral border of the scapula; action, draws scapula toward vertebral column. 



e) Splenius. A fairly broad but thin muscle on the back of the anterior part 

 of the neck under the anterior trapezius. (Running along its external surface 

 is a narrow straplike muscle, the rhomboideus capitis, see below.) Origin of 

 splenius, mid-dorsal line of neck and adjacent fascia; insertion, occipital region 

 of the skull and atlas; action, singly turns the head, together raise the head. 



Under the splenius are the epaxial muscles, continuations of those already 

 noted in the lumbar region. 



/) Supraspinatus. The superficial muscular layer of that part of the scapula 

 anterior to the spine consists of the pectoralis minor, which sweeps over the 

 scapula to be inserted on the spine and vertebral border. Lift up its anterior 

 border and separate it from the muscle beneath it. This muscle is the supra- 

 spinatus, filling the supraspinous fossa of the scapula. Origin, supraspinous 

 fossa; insertion, greater tuberosity of the humerus; action, extends the humerus. 



