370 H. W. NORRIS AND SALLY P. HUGHES 



across the dorsal border of the fourth interarcual muscle, then 

 farther ventrally along and across the elongate fifth epibranchial 

 bar, near the ventral end of the latter turning anteriorly to run 

 at the lateral border of the muscular wall of the digestive tract, 

 where it enters a ganglion (fig. 48). From the ganglion several 

 nerves pass anteriorly, apparently distributed to the wall of the 

 pericardial chamber. This anterior end of the ramus posttre- 

 maticus forms a so-called ramus cardiacus. 



As the fifth branchial nerve is passing across the interarcual 

 muscle a ramus pretrematicus is given off running posteriorly, 

 ventrally, and finally anteriorly along the anterior wall of the 

 fifth branchial cleft. Near the posterior border of the inter- 

 arcual muscle a ramus pharyngeus passes through the muscle 

 to the roof of the pharynx and has the usual distribution. 



Where the main lateral-line ganglion is in contact with the 

 visceral ganglion of the fourth branchial nerve (X3), a tract of 

 fibers passes from the former into the latter, thence out of the 

 ganglion along with the motor constituent and through the main 

 fourth branchial nerve into its posttrematic ramus. It contin- 

 ues in the latter around to the ventral part of the fourth branchial 

 arch. On the posterior border of the fourth ceratobranchial car- 

 tilage it leaves the posttrematic ramus through a small sympa- 

 thetic ganglion and passes anteriorly, ventrally, and mesially in 

 the fleshy connections of the fourth branchial arch with the 

 lateral trunk wall. It then turns posteriorly at the lateral 

 border of the coracobranchialis group of muscles, then farther 

 posteriorly runs along the lateral border of the coracoarcualis 

 muscle, and continues in this position, descending ventrally in 

 its course until the posterior lateral border of the pectoral girdle 

 is reached. Here it turns mesially around the pectoral girdle 

 and runs posteriorly in the ventral body wall, breaking up into 

 small twigs distributed to a small group of pit-organs situated 

 posterolaterally to the base of the yolkstalk of the embryo (figs. 

 48 and 50, vpo.). 



Of the occurrence in Squalus of 'rami pretrematici interni,' such 

 as are stated by Sewertzoff ('11) to be found in Scyllium, Acan- 

 thias, Raja, and Trigon, the writers find little evidence. Sew- 



