COMPARATIVE ANATOMY OF THE MUSCULAR SYSTEM 147 



Cat: 



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 forward from the middle of the back to the upper arm 

 is the latissimus dorsi. Origin, from the neural spines of the last thoracic and 

 most of the lumbar vertebrae and from the lumbodorsal fascia; insertion, by a 

 tendon on the medial surface of the humerus; action, pulls the fore limb dor- 

 sally and caudally. 



b) Trapezius muscles. There are three trapezius muscles in the cat; they 

 are the thin flat muscles covering the back and neck anterior to the preceding. 

 The posterior trapezius or spinotrapezius takes origin from the spines of the 

 thoracic vertebrae and passes obliquely forward, covering part of the latissimus 

 to be inserted on the fascia of the scapula; action, draws the scapula dorsad 

 and caudad. In front of this is the middle trapezius or acromiotrapezius . 

 Origin, neural spines of cervical and first thoracic vertebrae; insertion, meta- 

 cromion process and spine of the scapula and fascia of the preceding muscle; 

 action, draws scapula dorsad and holds the two scapulae together. The anterior 

 trapezius or clavotrapezius is the anterior part of the long muscle already described 

 as cephalobrachial. Origin, superior nuchal line and median dorsal line of neck; 

 passes obliquely ventrally to be inserted on the clavicle which is imbedded 

 on its inside surface; it is continuous with the clavobrachial muscle. Action, 

 draws the scapula dorsad and craniad. 



c) Levator scapulae ventralis. Carefully free the three trapezius muscles. 

 Along the ventral border of the acromiotrapezius and apparently continuous 

 with it is seen a fiat bandlike muscle which passes anteriorly diverging from the 

 acromiotrapezius and passing internal to the clavotrapezius which should be 

 cut across. Origin, transverse process of the atlas and occipital bone; inser- 

 tion, metacromion process and neighboring fascia; action, draws the scapula 

 craniad. 



d) Rhomboideus . Cut across the middle of the bellies of the spino- and 

 acromiotrapezius muscles. A thick muscle will be seen beneath them extending 

 from the vertebral border of the scapula to the mid-dorsal line; this is the 

 rhomboideus. Origin, neural spines of the vertebrae and adjacent ligaments; 

 insertion, vertebral border of the scapula; action, draws scapula dorsad. The 

 most ventral portion of this muscle is a practically separate muscle, the rhom- 

 boideus capitis, which extends as a slender band forward to originate from the 

 superior nuchal line; insertion, scapula; action, draws the scapula craniad and 

 rotates it. 



e) Splenitis. This is the large sheet of muscle covering the back of the neck 

 in front of the rhomboideus, internal to the trapezii and crossed by the rhom- 

 boideus capitis. Origin, from the mid-dorsal line and fascia; insertion, superior 

 nuchal line; action, raises or turns the head. 



