58 HUNTINGTON 



If the muscle forming the subject of this communication is 

 compared with the t}^pical siipraclaviciilaris or stcnioclavicu- 

 laris superior it will appear that the lateral attachment and the 

 relation to the clavicular head of the sterno-cleido-mastoid of 

 both agree. In our M. siipraclaviciilaris pro pr ins posterior 

 the lateral extremity of the muscle is attached to the posterior 

 surface of the clavicle, and it attains this position by passing 

 dorsad of the clavicular head of the sterno-cleido-mastoid. The 

 same arrangement obtains in those instances of the typical 

 sternoclavicjilaris in which the muscle extends further laterad 

 than is usually the case (Retzius' example, outer third of 

 clavicle), although in the majority of recorded cases the typical 

 sternoclavicular muscle is short, not extending beyond the inner 

 third of the clavicle. That the lateral end of the muscle here 

 under consideration extended beyond and behind the trape- 

 zius to the acromial end of the clavicle is therefore unusual 

 when compared with the typical arrangement of the steriio- 

 clavicularis, but it brings the entire group, to which both 

 muscles belong, into harmony with other muscular variations 

 which serve to satisfactorily explain the significance of the 

 aberrant condition. 



The mesal extremity of the muscle herein described differs 

 at first sight radically from the typical stcnwclavicularis . The 

 mesal tendon is attached behind the sterno-cleido-mastoid to 

 the posterior and upper border of the sternal extremity of the 

 clavicle, but entirely confined to that bone, not extending to 

 the sterno-clavicular capsule or to the manubrium. In contrast 

 to this arrangement the mesal tendon in the great majority of 

 the typical stcnioclaviciilares occupies a more ventral position, 

 being attached above and in front of the sterno-clavicular artic- 

 ulation to the manubrium. 



If, however, this typical arrangement of the mesal tendon of 

 the usual sternoclavicjilaris is compared with the variations re- 

 ported by Hyrtl, and with the cases described by Weber and 

 Tait, it will be seen that a series, depending upon regression of 

 the sternal extremity of the common form of the variant muscle, 

 can be established, leading from the usual type, through three 



