34O RAYMOND PEARL. 



by the N. accessorius, with, in some cases, fibers from the cer- 

 vical plexus going to the muscles of the ventral group. The 

 levator scapulae ventralis or omo-cleido-transversarius, pars ven- 

 tralis (Leche) belongs to an entirely different set of muscles than 

 those just considered. According to Leche 1 it is highly probable 

 that this muscle is a differentiation product of the muscle group 

 from which the M. levator scapulas comes. It is innervated by 

 fibers from the ventral branches of the spinal nerves. 



Evidently then, since the cleidomastoid and the levator scapulae 

 ventralis have such different sources the abnormality under dis- 

 cussion cannot be considered as a reversion. 



The abnormality does, however, seem to be suggestive as pos- 

 sibly giving us light on the meaning of the conditions found in 

 man with reference to the muscles of the ventral neck region. 

 In what manner will be apparent if the relations in man are con- 

 sidered briefly. The M. omotransversarius (i. e., levator scapulae 

 ventralis) is normally found in some form or other in practically 

 all mammals up to man. In man it is only occasionally present 

 as a separate muscle in abnormal cases. It has been a problem 

 how to account for the absence of this muscle under normal 

 conditions in man, and no satisfactory explanation for it has ever 

 appeared so far as is known to the writer. On the other hand 

 the human sternocleidomastoid is, of course, a complex muscle, 

 made up by the fusion of elements normally forming distinct and 

 separate muscles in the lower forms. Streissler 2 has shown that 

 this muscle contains at least the following elements : In the super- 

 ficial portion a sternomastoideus superficialis, a sterno-occipitalis 

 and a cleido-occipitalis element ; and in the deep layer a sterno- 

 mastoideus profundus and a cleidomastoideus element. 



The fact that occasionally the omotransversarius appears in 

 man as a distinct muscle may be taken as strong presumptive 

 evidence that in all cases the muscle is present in man as an 

 element in the ventral neck musculature. Why it is not found 

 under normal circumstances is because it is indistinguishably 

 fused with some other muscle. In the abnormal cases where it 

 does appear as a separate muscle we most probably have simply 



* Loc. /., pp. 731-735- 



* Loc. cit. 



