The muscles connecting the arm with the sternum, corresponding to the pectoralis muscles of man, fall into a considerable number of not always clearly separated bundles in the cat. We shall distinguish by name four such bundles; these might be, and frequently are, further subdivided. =M. pectoantibrachialis= (Fig. 65, _m_).--This is a small flat bundle about one or two centimeters wide, forming the most superficial portion of the pectoralis group. _Origin_ on the lateral surface of the manubrium. The muscle passes laterad onto the arm and is _inserted_ by a flat tendon into the superficial fascia of the dorsal border of the forearm, near the elbow-joint. The tendon is continuous craniad with the border of the clavobrachial (_k_), so that a bundle of fibres may pass from this muscle to be inserted with the clavobrachial, or a bundle from the clavobrachial to be inserted with this. The tendon is continuous caudad with that of the epitrochlearis (_r_). The fascia of insertion may be traced to an attachment into the dorsal border of the ulna. This muscle usually receives near its insertion a slip, sometimes called its caudal division, from the deep layer of the pectoralis major. _Relations._--Outer surface with the integument. Inner surface with both divisions of the pectoralis major (_l_) on its medial two-thirds, and with the biceps (_t_) and bicipital arch (_t′_) in its lateral one-third. The cranial border is closely applied to that of the clavobrachial (_k_), except at the two ends. _Action._--Draws the arm mediad. =M. pectoralis major=, or =ectopectoralis= (Fig. 65, _l_, _l′_).--In this it is usually possible to distinguish a superficial and a deep layer. The =superficial= (_l′_) layer is a flat band of fibres one or two centimeters wide. _Origin_ from a raphe in the midventral line, along the cranial half of the manubrium and for five to ten millimeters craniad of it. _Insertion_ (Fig. 81, _f_).--The pectoral ridge of the middle third of the shaft of the humerus, slightly dorsad of the line of insertion of the deep portion. _Relations._--Outer surface with the clavobrachial (Fig. 65, _k_) and integument, the medial end caudally with the pectoantibrachialis (_m_), and the distal end with the brachialis (_v_). Inner surface with the deep portion (_l_), the fibres of which it crosses obliquely. The =deep portion= (_l_) is a flat band of parallel fibres about three times as broad as the superficial portion. _Origin._--The ventral surface of the manubrium and of the first three divisions of the sternum, and the median raphe for about one centimeter craniad of the manubrium. It passes directly laterad.