2 oo 1'RACTICAL ANATOMY. 



\ i. The relation of subclavian artery and vein on first rib. 



12. A digitation of serratus magnus muscle on the first rib. 



13. Study the insertion of the scalenus posticus muscle on the outer surface 

 of the second rib. Also the digitations for the serratus magntis muscle on the 

 second. 



The Subclavius Muscle. Dissection of this muscle requires much care. 

 Cut the costo-clavicular ligament and the sterno-clavicular ligaments and then 

 lift the clavicle. This will bring the muscle into view. The muscle has a strong 

 sheath. Notice that the space between this muscle and the pectoralis minor is 

 bridged by the clavi-pectoral fascia. (Fig. 132.) Note the origin of the sub- 

 clavius from the first rib at the junction of its cartilage ; its insertion into a groove 



External 

 intercoBtals 



Internal 

 intercoBtals 



External 

 intercoBtala 



Internal 

 intercoBtals 



Infra-costales 



FIG. 140. THE INTKRI'OSTAI. MUSCLES. 



on the under surface of the clavicle, middle two-fourths. The structures you will 

 now see under the clavicle are: (i) The subclavius muscle and its sheath; (2) 

 the subclavian artery and vein ; (3) the brachial plexus of nerves. 



The scaleni muscles are three in number anticus, medius, and posticus. 

 A few movements of the forceps will develop their insertions two into the first 

 and one into the seconcf rib. 



The intercostal muscles and fasciae occupy the intercostal spaces. The 

 intercostal spaces are eleven on each side. Each space is occupied by : (i) Ex- 

 ternal and internal intercostal muscles ; (2) external, middle, and internal inter- 

 costal fasciae ; (3) intercostal arteries, veins, and nerves. 



The external intercostal muscles are descending /. e,, their fibres pass 



