H. B. POLI.AftD. 



The relations of the last two nerves which proceed from the 

 cranium are of special interest. They are really spinal nerves. 



The eleventh nerve arises from the medulla almost under the 

 vagus roots, that is considerably forwards. It runs obliquely through 

 the cranial wall which must here be considered of vertebral origin 

 and before exit divides into two branches one of which passes upwards 

 and supplies muscles extending from the petrosum to the shoulder- 

 girdle, that is to the supraclavicle. The other branch passes down- 

 wards behind the gills and under the last gill slit, joins the larger 

 following nerve. It has no dorsal roots (figs. 12, 13). 



The twelfth nerve arises by 2 roots, a dorsal and a ventral. The 

 dorsal does not pass through the bone of the skull but interverte- 

 brally and then swells out to form a considerable and 

 clearly marked ganglion. Like a spinal nerve it then joins the 

 ventral root. The ventral root passes through the skull wall and on 

 its exit like the eleventh divides into 2 branches one of which passes 

 upwards to supply the neck muscles while the stouter passes down 

 and gives oft" 3 stems to the branchial plexus after which it passes for- 

 wards aud supplies the coracoarcuales. The greater portion passes on 

 and joins the eleventh aud the two conjoined supply the branchio- 

 mandibular or geniohyoid muscle. 



