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, o) 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, o], 

 and transversus abdominis (Fig. 69, /). 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. 



i . 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 r 

 miodeltoid, and possibly the clavobrachial, which is frequently 

 called clavodeltoid. 



M. spinodeltoideus (Fig. 75, e; Fig. 68, *'). 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,/), acromiotrapezius (Fig. 68, //), and 



