88 



BONES OF THE UPPER LIMB. 



compressed antero-posteriorly, are each divided by a shallow groove into two 

 condyles. 



Those of the middle row are four in number. Smaller than those of the 

 preceding set, they resemble them in form, with this difference, that their 

 proximal extremities present on the articular surface a slight middle elevation 

 and two lateral depressions, adapted to articulate with the condyles of the 

 first phalanges. 



The terminal or ungual phalanges, five in number, have proximal extremi- 

 ties similar to those of the middle row, but with a rough depression in front, 

 where the flexor tendons are inserted. They taper towards their somewhat 

 flattened and expanded free extremities, which are rough and raised round 

 the margins and upon the palmar aspect in the ungual process. 



SESAMOID BONES. A pair of sesamoid bones is placed in the palmar wall 

 of the metacarpo-phalangeal articulation of the thumb; and similar nodules, 

 single or double, are sometimes found in the corresponding joint of one or 

 more of the other fingers, most frequently of the index and little fingers. 



DEVELOPMENT OF THE UPPER LIMB. 



FIRST APPEARANCE OF THE LIMBS. The earliest traces of limbs in the human 

 embryo are observed in the fourth or fifth week as elevations of the ventral plates 

 on the sides of the body, tipped with a thickening of the cuticle. In the fifth 

 or sixth week there is distinguishable in each a laterally compressed expansion, the 

 rudimentary hand or foot, and a more cylindrical pedicle, the arm or leg. About 

 the eighth week the division into fingers and toes takes place, the pollex of each 



1 year. 15 or 16 years. 17 or 18 years. 



22 years. 



Fig. 79. OSSIFICATION OP THE SCAPULA. 



A, the scapula from a child of about one year old. 1, shows the large spreading ossifi- 

 cation from the primary centre. 2, the commencing nucleus in the coracoid process. 



B, the scapula from a boy of about fifteen or sixteen years. The coracoid process, 

 (represented as too much separate in the figure), is now partially united at its base ; a 

 nucleus, 3, has appeared in the acromion, and another, 4, at the lower angle. 



C, shows the condition of the scapula at seventeen or eighteen years of age ; a second 

 point, 5, has appeared in the acromion, and ossification has advanced into the ridge of 

 the base, 6. 



D, the scapula of a man of about twenty-two years of age ; the acromion and the ridge 

 of the base are still separate. A thin scale on the coracoid process and an epiphysis of 

 the glenoid head, which sometimes occur, have been omitted. 



