66 F. W. THYNG 



the communicating branch with the first cervical nerve, it passes 

 caudad to join a branch from the third. The junction occurs 

 dorsal to the internal jugular vein and forms the descendens 

 cervicalis which extends ventrally between the internal jugular 

 vein and jugular lymph sac (plates 5 and 6). The descendens 

 cervicalis joins the ramus descendens hypoglossi to form the ansa 

 (An.hyp.). 



On the right side (plate 3), beyond the communicating branch 

 with the first cervical nerve, the ventral primary divisions of the 

 second cervical bifurcates. One branch joins the third cervical 

 to form the descendens cervicalis, while the other passes ventrally 

 between the vagus and internal jugular vein to join the hypo- 

 glossus. The fibers passing direct to the hypoglossus, therefore, 

 reach the ansa by way of the ramus descendens hypoglossi. 



The ventral prunary division of the third cervical nerve also 

 differs on the two sides. On the right (plate 3) distal to the 

 communicating branch with the second cervical nerve, it divides 

 into a cephalic and a caudal branch. The caudal branch fur- 

 nishes medially the ramus descendens cervicalis; and laterally a 

 branch which unites with one from the fourth cervical to form the 

 supra-clavicular nerves {N?i. s-cL). 



On the left side the ventral division of the third cervical 

 (plate 2) also divides into two branches. The more cephalic of 

 these first gives off medially a branch which passes between the 

 vagus and jugular lymph sac to the ramus descendens cervicalis. 

 Then, continuing ventrally between the dorsal portions of the 

 internal jugular vein and adjacent lymph sac, it furnishes (plates 

 5 and 6) the great auricular {N.aur.vi.), small occipital, and 

 cutaneous colli (N.c.c.) nerves. The great auricular nerve 

 pierces the dorsal part of the cephalic segment of the saccus 

 jugularis, and here communicates with the ramus externus of the 

 accessory nerve. The small occipital and cutaneous colli nerves 

 appear a little more caudally between the two cephalic segments 

 of the lymph sac. At the place of origin of the small occipital 

 and the cutaneous colli, the third cervical nerve has a communi- 

 cating branch with the fourth cervical, probably to assist in the 

 formation of the supraclavicular nerves {Nn.s-cl.) as on the 



