MUSCULAR SYSTEM. 115 



brse, and the ribs; inferiorly, with the pectoral, muscles; ante- 

 riorly, with the splenius; and superiorly, with the latissimus 

 dorsi. 



Dh-ectio)i. — The fibres converge from their various circum- 

 ferent attachments, like the leaves of a fan, to one common focal 

 point, which is its insertion into the scapula. 



Structure. — It is covered by a thin aponeurosis which is at- 

 tached around, principally, to the ribs. The costal portion is 

 fleshy and digitated ; the cervical portion is also fleshy ; but the 

 part fixed to the scapula is mostly tendinous. The muscle is 

 considerably thicker in the middle than around the circumference. 



Action. — It forms the principal agent of support to the trunk, 

 maintaining it and the shoulder in close apposition. This pair of 

 muscles are more or less concerned in all the motions of the sca- 

 pula; and will become dilators of the chest whenever they are 

 exerted while the limbs remain fixed points. 



INTERCOSTALES EXTERNI. 



Number. — Seventeen on each side. 



Sitttatio7i.—F\\\'mg up the intercostal spaces, outwardly: 

 reaching from the articulations of the ribs with the transverse 

 processes as far as the commencement of their cartilages. 



Attachment. — Anteriorly, to the external edge of the posterior 

 border of one rib ; posteriorly, to the internal edge of the anterior 

 border of the rib immediately behind the former. 



delations. — On the outer side, with the serratus, pectoral mus- 

 cles, obliquus externus, and transversalis and superficialis costa- 

 rum; on the inner side, with the intercostales interni ; supe- 

 riorly, with the levatores costarum. 



Direction. — Oblique : from before, backward; and from above, 

 downward. 



Structure. — Thick layers of united fleshy fibres included be- 

 tween broad aponeurotic slips of tendon, and in places displaying 

 tendinous intersections. 



INTERCOSTALES INTERNI. 



Number. — The same as the preceding. 



Situation. — Underneath the externi ; within the intercostal 

 spaces, reaching from the angles of the ribs to the sternum. 



Attachment. — To the antero-internal edge of the border of 

 one rib ; to the postero-internal edge of the rib immediately 

 before it. 



Relations. — On the outer side, with the preceding muscles, 

 and with the intercostal vessels and nerves; on the inner side, with 

 the pleura. 



