CoGHiLL, Cranial Nerves of Amblystovia. 245 



space between the m. sterno-hyoideus and the m. hyo-tracheah's, 

 in close relation with the ventral rami of the first and second 

 spinal nerves. Near the flexure cephalad, the r. recurrens 

 gives off a twig {rec. i) which penetrates the m. hyo-trachealis 

 and innervates the constrictor and dilator muscles of the glottis. 

 This twig may send fibers, also, to the m. hyo-trachealis and 

 m. dorso-trachealis. 



At the transverse level of the glottis, the r. recurrens sends 

 a twig (rec. X, 2.) of thinly medullated fibers laterad, which 

 enters the fourth branchial arch and turns cephalad ventrally of 

 the cartilage. It then turns dorsad on the lateral side of the 

 cartilage and innervates the dorsal epithelium of the gill arch. 

 It corresponds in its distribution to the second sensory intra- 

 branchial division of the post-trematic rami of the branchial 

 trunks of the vagus {X, ibr. g and X, 2br. S'). 



At various intervals along its course the r. recurrens sends 

 fibers to the m. hyo-trachealis; and along its terminal portion 

 to the m. interbranchiales (;rr. X, j). Anteriorly of the 

 tracheal muscle, the terminal fibers of the nerve ascend along 

 the mesial side of the fourth branchial cartilage to the epithe- 

 lium of the floor of the pharynx. These fibers function as the 

 terminal portion of the typical post-trematic ramus. 



VI. The First Two Spinal Nerves. 



T/ie first spinal nerve arises by two ventral roots. The 

 second root leaves the ventral side of the cord at the transverse 

 level of the posterior end of the fourth ventricle. The first 

 root arises some distance anteriorly of this. The two roots 

 pass out of the neural canal together through a foramen in the 

 first vertebra. 



The first ramus of the first spinal nerve [sp. i, r i) leaves 

 the nerve immediately outside the foramen. It passes cephalad 

 entally of the musculature and crosses the dorsal surface of the 

 ganglion IX+X. It is distributed to the anterior portion of the 

 m. extensor dorsi communis 



The ventral ramus [sp. i v.) leaves the nerve at about the 

 same level as the first ramus. It inclines ventrad and caudad 



