PERICLAVICULAR SUPERNUMERARY MUSCLES 55 



ment to both extremities of the clavicle the muscle described in 

 this paper belongs to the rctro-clavicnlar group and possesses 

 hence an entirely different morphological significance. The fol- 

 lowing instances have been observed of supraclavicular muscles 

 situated behind the sterno-cleido-mastoid and trapezius. 



M. J. Weber (Vollstandiges Handbuch der Anatomic des 

 Menschlichen Korpers (Zergliederungs-Kunde und Kunst), I 

 Bd., Bonn, 1839, p. 560) says : 



" I have observed once a variation, remarkable on account of 

 the analogy of the clavicles and ribs, and of the subclavius with 

 the intercostals, in which from the posterior surface of the 

 manubrium sterni to the post, surfaces of the sternal ends of 

 both clavicles a fairly strong semicircular flat muscle passed 

 which could depress the clavicles down and in." 



Lawson Tait (Journ. of Anat. and Phys,, p. 237) described 

 a muscle arising by two heads, one from the posterior surface 

 of the manubrium sterni at its junction with the cartilage of the 

 first rib, the other from the posterior edge of the first rib itself. 

 It lay on the brachiocephalic trunk, on the lower thyroid veins 

 and the scalenus anticus, and was inserted into the clavicle, 

 along the posterior border of the bone, at the inner margin of 

 the insertion of the trapezius. 



Knott is quoted as having observed a muscle identical in all 

 respects with that described by Tait. 



These two instances of Weber and Tait are quoted by most 

 authors treating of the periclavicular supernumerary muscles 

 under the name of M. retrodavicidaris or stcnioclavicularis pos- 

 terior. Macalister (''Additional Observations on Muscular 

 Anomalies in Human Anatomy (Third series), with a cata- 

 logue of the principal muscular variations hitherto published," 

 Trans. Royal Irish Acad., Vol. XXV, Pt. I, Dublin, 1872, 

 p. 51) quotes Weber's and Tait's cases as instances of the " M. 

 retroclavicularls " and adds concerning the latter's case : " This 

 is much rarer than the foregoing (M. supraclavicularis of 

 Luschka and Haller, cf infra), and is probably only a form of 

 the M. supraclavicularis given above." 



Both Testut (" Les anomalies musculaires chez I'homme," 



