THE THORAX. 



ANTERIOR AND LATERAL WALLS. 



Locate (i) the sternum, presternum, mesosternum, metasternum. (2) The 

 suprasternal notch and the interclavicular ligament. (3) *Find the pronounced 

 elevation between the first and second pieces of the sternum. This is the manu- 

 brio-gladiolar joint, and is the point concerned in the rule for counting the ribs. 



TUBERCLE 



] icvator costse and 

 accessor! us 



Scalenus medius 



GROOVE FOR SUBOLAVIAN 

 ARTERY 



Scalenus aaticus 



GROOVE FOR SUBCLAVIAN 

 VEIN 



Levator costae 

 Accessorius 



(insertion) 

 Cervicalis ascendena 



<origin) 

 Serratus posticus 



superior 



(insertion) 



Scalenus posticus 



Third digitation of 

 serratus magnus 



External 

 intercostals 



FIG. 138. FIRST AND SECOND RIBS. 



Rule : this ridge corresponds to the cartilage of the second rib. (4) Find the 

 sterno-clavicular articulation. See if it is freely movable, as it should be. Note 

 when you dissect this region the presence of an interarticular fibre-cartilage, 

 dividing the synovial cavity into two compartments an inner and an outer. (5) 

 Note that seven true ribs articulate by their cartilages with the sternum ; that all 

 except that of the first rib are movable. (6) Examine the metasternum or 

 ensiform process to see its deflection, whether lateral, forward, or posterior. 

 (7) Count the ribs and study the nature of the chondro-costal articulation. 



198 



