A STUDY OF THE SKELETON 169 



see how the arm is attached to the rest of the skeleton. Ly- 

 ing outside the ribs at the anterior end of the trunk are two 

 flat, triangular shoulder blades (each called a scap'u-la) (Fig. 64, 

 scap) and two slender collar bones (each called a clavicle) 

 (Fig. 64, cf). The /-shaped collar bones are attached ven- 

 trally to the breastbone, while the other end of each is 

 joined to one of the shoulder blades. In this way an incom- 



5LV ,M disc 



is 

 FIG. 70. Bones of the Pelvic Girdle (Ventral View). 



acet = socket of pelvic bone into which fits head of femur, 

 cocc = coccyx. disc cartilage disk between vertebrae. 



il, is, pu = parts of pelvic bone. sac = sacrum. 

 5LV= fifth lumbar vertebra. 



plete circle of bones is formed to which is given the name 

 pec'to-ral girdle (Latin pectoralis, referring to the chest). A 

 shallow socket is found on the outside of each shoulder 

 blade, and into this fits the proximal end of a humerus 

 bone. It will be seen that the pectoral girdle is directly 

 attached to the rest of the skeleton only by the ventral 

 ends of the collar bones. Great freedom of motion for the 

 arms is therefore possible, since the girdle itself is movable. 



