90 TRANSACTIONS OF THE [jAN. 11, 



M. Genio-hyoideus = CII. 



M. Thjro-hyoideus = CII. 



M. Sterno-thyroideus = CI. (Fig. VIII.). 



M. Sterno-hyoideus = CI. + CIII. 



M. Omo-hyoideus = CI.+ CIII. 



The anatomical divisions of the loop would be : 



I. Ventral limb (CI. Descending trunk), (CII. Ascending 

 trunk.) 



II. Dorsal limb (CII. and CIII.). 



III. Triangular precarotid interlacement. 



IV. Terminal descending trunk (CI. and CIII.). 



In considering the significance of the above detailed associa- 

 tion of the upper three cervica) nerves with each other, and of 

 the First and Second with the Hypoglossal, the following facts 

 suggest themselves : 



The morphology of the Infra-hyoid group of muscles in Man 

 reveals only exceptionally the more intimate connection with 

 the tongue proper which appears in many of the lower forms. 



The known facts may be grouped in reference to the individul 

 muscles as follows : 



Sterno-hyoid. 



This muscle is at times found united with the Sterno-th3'roid 

 in man. In mau}'^ animals this connection — partial, especially 

 near origin, or complete — is normal — as in Ruminants: Mono- 

 tremata, most Carnivoi'a : Myrmecobivs, Erinacevs, Lepiia, 

 Manatus, several Frosimians : Ateles, Lagothrix, etc. In all 

 these forms the muscles are more or less closely united at their 

 lower part. 



In the Horse (Chaveau) they are only separate at the level of 

 the aponeurotic intersection. Testut finds the two united in 

 the Bear up to within 3 cm. of the larynx. 



In Ornitliorhynchus the Sterno-hyoid is not present as a dis- 

 tinct muscle, but is represented by fasciculi which separate from 

 the Sterno-thyoid to pass to the Hyoid bone. 



Instances in Avhich the muscle does not present any connec- 

 tion with the Hj'oid bone, but passes beyond the same to join 

 some of the muscles of the Hyo-maxillary group, are numerous, 

 and of particular interest in reference to the connection between 

 the proper motor nerve of the tongue and the nerve supply of 

 the Infra-hyoid group of muscles. 



In Echidna (Westling) the muscle arises from the xiphoid 

 cartilage and by a narrow attachment from the Corpus stern i, 



