THE UPPER EXTREMITY. 



The Shoulder-Girdle. — This consists of the clavicle and scapula. The latter 

 is far the most important morphologically, representing, as it does, both the scapula 

 and the coracoid of the lower classes of vertebrates ; while the clavicle is inconstant 

 in mammals, and seems to be no part of the primitive shoulder-girdle. The scapula 

 bears the socket for the humerus. It hae no bonv attachment to the trunk save 

 through the clavicle, which,' interposed between it and the sternum, is connected 

 with both by joints. 



THE SCAPULA. 



Physiologically,- the essential part of the scapula is the socket for the shoulder ,• 

 a part of this is made by the coracoid element, which in man is an insignificant pro- 

 cess of the shoulder-blade. The secondary functions of the bone are to give origin 

 to some muscles and to afTord leverage to others for their action on the arm. In 

 most mammals the scapula may be considered a rod running upward from the joint, 

 from which three plates expand, one towards the head, one towards the tail, and one 

 outward. In man the second of these plates points downward and is excessively 

 developed. It is more convenient in man to speak of one main plate, the body of the 

 scapula, with the spine springing from the dorsal surface. 



The body is triangular, with two surfaces, — a ventral one towards the ribs and 

 a free dorsal one, — three borders, and three angles. 



The posterior or vertebral border,' sometimes called the base, is the longest. 

 It is nearly vertical from the lower angle to a triangular space on the dorsum, oppo- 

 site the origin of the spine, above this it, as a rule, slants forward, but at a very 

 varying angle. The upper border'^ slants downward and forward to iki^ supra- 

 scapular notch ^ at the base of the coracoid process. This notch, transmitting the 

 suprascapular nerve, is sometimes imperceptible, but usually is well marked and 

 sometimes very deep. It is bridged by a ligament, which may be replaced by bone, 

 transforming the notch into a foramen. The anterior or axillary border* is the 

 only thick one. Just below the glenoid cavity it begins as a triangular roughness 

 for the long head of the triceps. This is continued as a line which ends on the 

 dorsal surface near the lower angle, a little above an unnamed process curving for- 

 ward and inward from which a part of the teres major arises. This is the analogue 

 of a process much developed in some small monkeys. It is sometimes very large, 

 the increase of size being in no relation to that of the bone nor of the muscle. 

 Above this on the anterior border there is a deep groove for a part of the sub- 

 scapularis muscle just internal to the anterior edge proper. Below the process the 

 border runs downward and backward to the inferior angle. ^ This angle is some- 

 times very sharp, sometimes quite the reverse. The same, in a less degree, may 

 be said of the upper angle,* usually sharp, sometimes squarely truncated. The 

 anterior angle " is the glenoid cavity. This, with the base of the coracoid process, 

 is called the head of the scapula, the neck being a constricted region behind it, 

 reaching to che suprascapular notch. The glenoid cavity ** is an oval, slightly 

 hollowed, cartilage-covered surface expanding from a narrower base. The long axis 

 is vertical and the broad end below. There is often an indentation at the upper 

 part of the inner margin. The edge is a little raised where it bears the glenoid 

 ligamcfit, which deepens the cavity for the reception of the head of the humerus. 

 The top of the edge forms the supraglenoid tubercle, whence starts the long head of 

 the biceps. 



The coracoid process springs from the top of the head just behind the glenoid 

 cavity and a little to the inner side. The first part, or root, which is compressed 

 from side to side, rises inclining somewhat inward. The second, the free projecting 

 portion, irregularly cylindrical, runs forward, rather outward and downward, to end 

 in a knob near the inner side of the shoulder-joint. The upper and inner surface is 



' Margo vertebralis. ' M. superior. ^ locisura scapniae. ^ M. axillaris. ' Angulus inferior. ''A. medialis. ' A. lateralis. 

 'Cavitas glcnoidalis. 



248 



