156 THE MUSCLES. 
and fourth costal cartilages it ends in a thin tendon which 
passes beneath the transversus costarum and is 
Inserted into the first costal cartilage near its middle, into 
the second costal cartilage near its sternal end, and into the 
sternum between the first and fourth cartilages. 
Relations.—Outer surface of the cranial part of the muscle 
and its tendon with the pectoralis minor (Fig. 68, 0) and the 
transversus costarum (Fig. 73,7); caudad the muscle is covered 
by the outer layer of the rectus sheath. Lateral edge with the 
obliquus externus (Fig. 68, ), obliquus internus (Fig. 73, 0), 
and transversus abdominis (Fig. 69, 7). Medial edge with the 
muscle of the opposite side. Inner surface with the internal 
intercostals (Fig. 69, £) and the rib cartilages; the inner layer 
of the rectus sheath and the peritoneum. 
Action.—Retracts the ribs and sternum and compresses the 
abdomen. , 
IV. MUSCLES OF THE THORACIC LIMBS. 
The muscles connecting the thoracic limbs with the rest of 
the body have been described. 
1. Muscles of the Shoulder. 
A. MUSCLES ON THE LATERAL SURFACE OF THE 
SHOULDER. 
M. deltoideus.—The deltoid muscle of the cat is divided 
into two (or three) portions which are together equivalent to 
the human deltoid. These are the spinodeltoid, the acro- 
miodeltoid, and possibly the clavobrachial, which is frequently 
called clavodeltoid. 
M. spinodeltoideus (Fig. 75, ¢; Fig. 68, 2).—A rather 
thick, flat muscle between the scapular spine and the deltoid 
ridge of the humerus. It forms a chord of the angle between 
the glenoid border of the scapula and the humerus. 
Origin by short tendon-fibres from the glenoid border of 
somewhat more than the middle third of the spine of the 
scapula (Fig. 76, g), and from a tendinous raphe between the 
spinotrapezius (Fig. 68, 7), acromiotrapezius (Fig. 68, /%), and 
