MUSCLES OF THE TRUNK. 298 



divides this muscle into two portions, which he designates the sterno-radialis and small sterno- 

 humeralis.) 



Situation — Composition. — This muscle is situated between the two anterior 

 limbs, occupies the inferior surface of the chest, and is formed by two portions 

 which adhere closely to each other, but are yet perfectly distinct. Following 

 the example of Girard, we will describe these as two particular muscles by the 

 names of sterno-humeralis, and sterno-aponeuroticus . 



A. Sterno-humeralis (Pectoralis ksT\G\5^).— Form— Structure.— T\A% is 

 a short, bulky muscle, flattened above and below, contracted at its termination, 

 and composed almost entirely of thick parallel fibres. 



Direction and Attachments. — It commences on the anterior appendage and 

 the inferior border of the sternum, and is directed obUquely backwards, down- 

 wards, and inwards, to reach the anterior ridge of the humerus, where it 

 terminates by an aponeurosis corumon to it, the mastoido humeralis, and the 

 sterno-aponeuroticus. 



Relations. — Externally, to the skin, from which it is separated by connective 

 tissue, and to the inferior extremity of the cervical panniculus ; internally, to 

 the sterno-aponeuroticus and sterno-prescapularis. Its anterior border forms, 

 with the mastoido-humerahs, a triangular space occupied by the subcutaneous, 

 or " plate," vein of the arm. 



Action. — It acts principally as an adductor of the anterior limb. 



B. Sterno-aponeuroticus (Pectoralis Transversus). — Form — Structure 

 — Direction — Attachments. — A very wide, thin, and pale quadrilateral muscle 

 formed of parallel fleshy fibres, which arise from the entire inferior border of 

 the sternum, to pass at first outwards, then downwards, and terminate in the 

 following manner : the anterior fibres go to the aponeurosis which attaches the 

 mastoido-humeralis and pectoralis anticus to the anterior ridge of the humerus ; 

 the posterior fibres are also continued by a very thin fascia, which is spread 

 inside the limb to the external face of the antibrachial aponeurosis. 



Relations. — By its superficial face, with the skin, which adheres intimately to 

 it by means of dense connective tissue, and with the pectoralis anticus, which 

 covers its anterior border. By its deep face, with the two portions of the other 

 pectoral, the flexor brachii, and the long extensor of • the forearm ; it also 

 responds, by this face, to the antibrachial aponeurosis and the subcutaneous vein 

 of the forearm, which it maintains applied against that aponeurosis. 



Action. — It is an adductor of the anterior limb, and a tensor of the anti- 

 brachial aponeurosis. 



2. Deep Pectoral (Pectoralis Magnus and Parvus) 

 (Figs. 174, 11, 13 ; 175, 1). 



Synonym. — The pectoralis parvus of Man 



Volume — Situation — Composition. — An enormous muscle, situated beneath 

 the thorax, and composed, like the preceding, of two perfectly distinct portions, 

 described by Girard as two muscles, and designated by him as the sterno- 

 trochineus and sterno-prescapularis. 



A. Sterno-trochineus. — Pectoralis magnus of (Percivall, Rigot, and) 

 Bourgelat. (The great sterno-humeraUs of Leyh.) 



Volume — Extent. — This muscle, the largest of the two, is considerable in 



