170 



The Development of the Arm in Man 



mass of condensed tissue along the vertebral border, and at the posterior 

 angle, the cartilage reaches to the level of the third rib and the condensed 

 tissue nearly to the fifth. The anterior border is somewhat irregular 

 and thickened and gives origin in part to the supraspinatus muscle. 

 The lateral lip of this border probably represents the spine and the 

 median lip the anterior border. Projecting from the lateral side of the 

 head and continuous with the lateral lip of the anterior border is the 

 acromion process. It is large, curved and mostly of condensed tissue 

 and contains a slender core of cartilage continuous with the cartilage 



trapezoid metacarpal 



trapezium 

 ( scaphoid 



OS magnum . 



ant. border 

 acromion , spine 

 coracoid ^ft^^. 



unciform 



,FiG. 12. Cartilaginous slceleton of tlie arm of embryo XLIII, lateral view. 

 X 20 diameters. 



of the body. The coracoid process arises from the median side of the 

 head, is larger than the acromion, and contains a much larger cartil- 

 ao-inous core, which is continuous with the cartilage of the body. The 

 acromio-clavicular ligament is strongly developed. 



The clavicle consists of a thick mass of condensed tissue, extending 

 from the acromion to the tip of the first rib, where it continues with 

 the half sternal anlage. There is no line of separation at either end. 

 There is a small core of a peculiar precartilaginous tissue. 



The Immerus is larger, longer and more slender in proportion to its 



