1897.] NEW YORK ACADEMY OF SCIENCES. 89 



loosel}" attached to it by connective tissue. The precarotid 

 communication is tiiangulai- in shape, the nerves composing the 

 triangle being easily' separated from each other and not enter- 

 ing into any true anastomosis at this point. The ventrally 

 l)laced base of the triangle is formed b3'the descending trunk from 

 the First Cervical, the upper (anterior) side by the ascending 

 branch from the Second Cervical, the lower (posterior) side by 

 the entire branch from the the Third Cervical, which at the in- 

 ferior (posterior) angle joins the trunk derived from the First 

 Cervical. The combined nerves proceed downwards overlying 

 the sheath of the Carotid vessels, and from the common trunk 

 branches are derived which pass to the Sterno-hyoid, Sterno- 

 thyroid and both divisions of the Omo-hyoid, the nerve to the 

 Sterno-thyroid being remarkablv long and continuing on the 

 deep surface of the muscle nearly to the sternal attachment. 



Fig. VII., of Plate YII., /epresents the plan of the deep cer- 

 vical ansa on the right side in a specimen of Macacus i^hesus 5 , 

 850.5 grm. bodyweight. 



The same general arrangement is here repeated, with the 

 trifling difference in the terminal distribution of the descending 

 trunk, which affords separate branches from the ventral border 

 to the Sterno-hyoid, Sterno-thyroid and the anterior belly of the 

 Omo-hyoid, the inferior continuation of the nerve then dividing 

 into an anterior branch for the lower portion of the Sterno- 

 thyroid, and a posterior division for the posterior part of the 

 Omohyoid. 



Fig. Till., of Plate YII., shows the plan of the ansa in 3Ia- 

 racKS sinicus, and, excepting a high origin of the nerve to the 

 Sterno-hyoid, presents the same arrangement as the preceding 

 forms. 



In the remainder of the series examined the conditions were 

 identical, differing only in the degree of ease with which the 

 course of the nerves engaged in the triangular precarotid inter- 

 lacement could be demonstrated, and in some minor details re- 

 garding the point of derivation of the terminal muscular branches. 



While in man the interlacing of the nerves in the h^'poglossal 

 and deep cervical loops is close and intimate, preventing the 

 complete separation of the individual nerve trunks, the com- 

 plete agreement as regards structure throughout the series of 

 Cj-nomorpha examined affords strong reasons for believing that 

 the ground-plan of the anastomosis is formed on the type pre- 

 sented by them, and that we will be obliged to modify the scheme 

 of the human loop, as indicated in Roll's sketch (Fig. Y.), ac- 

 cordingly. 



Expressed in terms of muscular equivalents the resolution of 

 the ansa would yield the following results : 



