MUSCLES OF THE CHEST. 597 



mechanical appliances, and that its appearance is very 

 different when viewed after having the upper extremities 

 detached. In this condition, with the arms removed, the 

 chest looks larger, as it really is, below than above, while 

 in the living state, or with the bony shoulder and arms ap- 

 pended to the skeleton, this cavity looks larger above than 

 below, which it is not. The chest is bounded, as stated, by 

 the sternum and costal cartilages in front, by the dorsal 

 vertebrae behind, the diaphragm below, the ribs and the in- 

 tercostal muscles laterally, and the superior opening of this 

 cavity, which is occupied by the passage through it of the 

 trachea, oesophagus, muscles, vessels, nerves, and cellular 

 tissue, above. It is also lined by a serous membrane, which 

 is reflected from its interior walls over the lungs and peri- 

 cardium, called the pleura. All these parts have been de- 

 scribed elsewhere, except the muscles on the anterior walls 

 of the chest and pleura, which we shall now proceed to 

 notice. 



SECTION I. 



MUSCLES OF THE CHEST. 



Dissection. Make an incision through the integuments 

 from the upper edge of the sternum along the median line to 

 the xiphoid cartilage. From the upper end of this incision 

 carry a second along the clavicle to the acromion process, 

 and from its lower end a third along the lower margin of 

 the great pectoral muscle, which is readily seen, to the 

 humerus. Kaise the integuments by commencing the dis- 

 section along and in the direction of the third incision for 

 the right side, and from the second incision for the left 

 side. This will be exposing the great pectoral muscle in 

 the direction of its fibres. A superficial fascia will be 

 raised at the same time with the integuments, which is 

 both delicate and cellular, and continuous above with the 

 superficial fascia upon the neck, and below with the same 

 upon the abdomen. 



The Pectoralis Major (Fig. 167) arises fleshy from th 

 anterior two-thirds of the clavicle, tendinous from the an- 



