452 THE ASCENT OF MAN. 



accordingly degeuerated, being represented by a strip of fascia. Very 

 often however, a few muscular fibers are still found in this situation. 



Several minor peculiarities that remind us of primitive conditions 

 occur in the region of the humerus. Occasionally a .supracotxJyIoid 

 process is fouiul, throwing a protecting arch over the brachial artery 

 aiul median nerve; in this resembling the supracondi/loid foramen of 

 marsupials. Struthers found this to be hereditary, occurring in a father 

 and four children. A perforation of the olecranon fossa, the pit at the 

 lower end of the humerus into which the beak-like end of the ulna fits 

 when the arm is fully extended, may probably be regarded as a rever- 

 sion toward the condition of anthropoid apes. This frequently occurs 

 in South African and other low tribes and in the men of the stone age. 

 Kecently Dr. D. S. Lamb has found it remarkably frequent in prehistoric 

 Indian humeri from the Salado Valley, Arizona. 



While the region of the hand and fore-arm indicates increase of 

 specialization, the upper part of the limb generally testifies to a regres- 

 sion from a former more highly developed state. The anatomy of the 

 liyiug apparatus of a bird shows a series of muscular, ligamentous, and 

 bony structures connected with its upper arm far beyond anything 

 ever seen in man. The coracoid bone, a very important element of the 

 shoulder girdle in birds, has become reduced in man to a little vestigial 

 ossicle that about the sixteenth year becomes soldered to the scapula 

 as the coracoid i)rocess. The muscles arising from this, — pcctoralis 

 minor, coraco-brachiaUs, and biceps, — are structures represented in birds 

 by strong, flying muscles. The subclavius, a little slip ending at 

 the clavicle, appears to have formerly passed to the coracoid bone or 

 to the humerus and been employed in arm movement. The j^^cforalis 

 major appears to represent what was formerly a series of muscles. All 

 these have a tendency to repeat their i)ast history, and the number of 

 variations found among tijem is legion. The biceps show traces of its 

 former complexity by appearing with three, four, or even five heads, 

 by a great variety of insertions, by sending a tendon outside the joint 

 capsule instead of through it, as is the rule. The pectoralis major may 

 break up into several different muscular integers, inserted from the 

 shoulder capsule down to the elbow. The coracobrachiaUs shows the 

 same instability, an<l by its behavior clearly indicates its derivation 

 from a much larger and more extensive muscular sheet. 



Not less significant are the ligaments about the shoulder. Many of 

 these appear to be relics of organs found active in animals lower in the 

 scale. Thus the coraco-acromial ligament spanning over the shoulder 

 joint is probably a former extension of the acromion process ; the rhom- 

 hold, conoid, trapezoid, and (jlenohumeral ligaments represent regres- 

 sive changes in the suhclarius muscle, the coracohumcraJ ligament, a 

 former insertion of the pectoralis minor. Bands of the deep cervical 

 fascia alone remain to testify to the former existence of the levator clav- 



