148 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



/) Supraspinatus. On turning back the ventral half of the cut acromio- 

 trapezius a stout muscle is seen occupying the supraspinous fossa of the scapula. 

 Origin, whole surface of the supraspinous fossa; insertion, greater tuberosity 

 of the humerus, next to the insertion of pectoralis minor; action, extends the 

 humerus. 



g) Deltoids. There are two deltoids in the cat. The clavobrachialis already 

 described is sometimes also considered as a deltoid and is called the clavodeltoid 

 by some authorities. The acromiodeltoid is a short thick muscle passing ven- 

 trally from the acromion process; it is inserted on the surface of other muscles 

 of the shoulder. It lies lateral to the clavobrachial. Action, with the next. 

 Turn the flap of the acromiotrapezius forward again. Posterior to the line 

 marking the insertion of the acromiotrapezius and the levator scapulae ventralis 

 is a muscle which passes to the upper arm, across the upper ends of the muscles 

 of the upper arm. This is the spinodeltoid. Origin, spine of the scapula; 

 insertion, ridge (deltoid ridge) of the humerus, the insertion being concealed 

 by the acromiodeltoid; action, the deltoids raise and rotate the humerus. 



h) Infraspinatus. Cut across the belly of the latissimus dorsi. Bring the 

 anterior parts of the latissimus and the spinotrapezius forward so as to expose 

 the posterior part of the scapula. Two large muscles are here seen. The ante- 

 rior one fills the infraspinous fossa of the scapula, from whose surface it takes 

 its origin and is inserted on the greater tuberosity of the humerus, the insertion 

 being concealed by the deltoids which may be cut across to see it. This muscle 

 is the infraspinatus. Action, rotates the humerus. 



i) Teres major. The stout muscle immediately behind the preceding, its 

 fibers running in the same direction. Origin, axillary border of the scapula and 

 fascia of neighboring muscles; insertion, in common with latissimus dorsi on 

 the medial surface of the humerus; action, rotates the humerus, and lowers it. 



j) Teres minor. Carefully separate the infraspinatus from teres major and 

 separate the former from the deltoids and the muscles of the upper arm. On 

 the posterior border of the infraspinatus and somewhat covered by it is the small 

 teres minor. Origin, axillary border of the scapula ; insertion, greater tuberosity ; 

 action, assists the infraspinatus. 



k) Subscapularis. Place the finger under the anterior border of the scapula 

 and clear away connective tissue from the under surface of the scapula. The 

 subscapular fossa is seen to be occupied by a muscle, the subscapularis, which 

 covers the inner or medial surface of the scapula. Origin, subscapular fossa; 

 insertion, lesser tuberosity of the humerus; action, pulls the humerus medially. 

 Posterior to the subscapularis will be found part of teres major which extends 

 to the medial surface of the scapula. 



/) Serratus ventralis (anterior). Cut through the rhomboideus close to the 

 vertebral column. The scapula then swings loose. On raising the scapula, a 

 large fan-shaped muscle is seen extending from the vertebral border of the 



