MUSCULAR ABNORMALITY IN THE CAT. 339 



of M. deltoideus of earlier writers) caudoventrad. At its inser- 

 tion the cleidomastoid lies entirely beneath the clavotrapezius. 

 Lying close besides the cleidomastoid (dorsad and in part 

 mediad) is the M. levator scapulae ventralis ( = M. omo-trans- 

 versarius Streissler, loc. cit., = Pars ventralis of the M. otno- 

 cleidotransversarius Leche, loc. cit., = " omo-trachelien " Le 

 Double, loc. cit.\ This muscle in the cat takes origin by two 

 heads, one coming from the basis cranii opposite the middle of 

 the bulla tympani, and the other from the ventral surface of the 

 transverse process of the atlas. 



In a well-developed adult female cat dissected by the writer, 

 the following abnormal relation of the cleidomastoid and the 

 levator scapulas ventralis was found on the left side of the body. 

 At almost precisely the middle point of the levator scapulae ven- 

 tralis a thick muscle band, approximately 4 mm. wide, passed 

 from the ventral border of this muscle cranioventrad to the dorsal 

 border of the M. cleidomastoideus, with which muscle it joined. 

 The connecting band was throughout its length of approximately 

 the same thickness as the Mm. cleidomastoideus and levator 

 scapulae ventralis at the places where it joined them. 



In considering the significance of this abnormality the possi- 

 bility of its representing a case of reversion may be dismissed at 

 once, because in their comparative anatomy the cleidomastoid 

 and levator scapulae ventralis are known to be quite distinct 

 muscles. The M. cleidomastoideus is a differentiation from the 

 general sternocleidomastoid group of muscles, which in turn is 

 to be considered as having separated from the trapezius group. 1 

 It belongs to the rather thin, superficial sheet of muscle which 

 covers the dorsal, lateral and part of the ventral surface of the 

 neck, and the dorsal surface of the cranial thoracic region in all 

 the Mammalia. This sheet of muscle breaks up into varying 

 numbers of separate muscles in different groups. All of these 

 muscles, however, as has been very clearly brought out by 

 Streissler (loc. cit.), fall into either a dorsal or a ventral group. 

 The dorsal group may be characterized as the dorso-scapularis- 

 trapezius group, and the ventral as the sternocleidomastoid group. 

 All the muscles of this superficial layer are innervated primarily 



1 Cf. Leche, loc. cit., pp. 701-706. 



