34 Anatomy Applied to Medicine and Surgery. 



its insertion and the practical application thereof. It is 

 a triangular muscle with the base internally and the apex 

 externally, and is composed of two distinct parts one 

 attached to the anterior surface of the sternal half of the 

 clavicle the clavicular portion, and the other the chon- 

 dro-sternal portion, to half the breadth of the sternum, the 

 cartilages of the true ribs with the exception of the ist, 

 yth, etc. The interval between these portions is more or 

 less distinct, and may be represented by a line drawn 

 from the sterno-clavicular articulation, when the arm is 

 at right angles to the body, to the middle of the two 

 condyles of the humerus. This muscle is inserted into 

 the anterior bicipital ridge of the humerus by means of a 

 broad tendon composed of two flat planes, or lamellae an 

 anterior and a posterior. The anterior the thicker 

 receives the clavicular portion of the muscle as well as 

 the upper half of the chondro-sternal portion, and the 

 fibres are inserted into this anterior lamella in the order 

 of their origin from clavicle and sternum. Passing oblique- 

 ly downwards and outwards, the anterior lamella crosses, 

 in a manner somewhat like the letter "X," the posterior 

 lamella which passes obliquely upward and outward- 

 The posterior lamella has inserted into it the lower half 

 of the chondro-sternal portion and in addition some deep 

 fibres from the cartilages of the 5th and 6th ribs. 



This crossing of the planes permits the upper fibres 

 to be inserted as low down on the humerus as the inser- 

 tion of the deltoid, while the lower fibres of the muscle 

 are inserted as high up on the bone as the subscapularis, 

 viz: about half an inch below the lesser tuberosity. This 

 is brought about by means of a twisting of the fibres of 

 the lower part of the muscle, and especially of the deep 

 fibres. The above is the usual arrangement, though it is 

 subject to considerable variation, as, for instance, on two 



