178 WILLIAM F. ALLEN 



fective or motor fibers. It is also apparent from figure 5 that 

 branches from the ventral bundle of the vagus^ innervate the 

 immediate region. Dorsal branches, rami pharyngei or oeso- 

 phagei (fig. 5, R.Oes.) pass dorsally at first along the outer sur- 

 face of the M. constrictor pharyngis, then bend caudally to 

 follow the dorso-lateral surface of the oesophagus or pharynx. 

 Ventral branches (fig. 5, R.M.C.P. (1) ) leave the ventral bundle 

 to supply the posterior division of the M. constrictor pharyngis 

 and the connective tissue outside. No connections were noted 

 between the spinal nerves and the vagus as has been described 

 by Johnston ('05) for Petromyzon. 



From ordinary haematoxylin preparations the nerve cells in 

 the vagus nerve have every appearance of being bipolar, having 

 probably one peripheral and one central process. Although no 

 silver or methylen blue preparations were available, the writer 

 is unable to see any reason for regarding these cells as sympa- 

 thetic cells. Apparently we have in the vagus and glosso- 

 pharyngeal nerves in Polistotrema the same tendency for the 

 nerve cells of the neural crest to migrate peripherally as in the 

 spinal nerves. This may represent a partial repetition of a 

 more primitive condition, which possibly dates back to the 

 diffuse condition of nerve cells found in some invertebrates. 

 Parts of this system likely survive in the higher vertebrates to 

 become differentiated into the sympathetic system, while other 

 cells are collected in the head region as the cranial ganglia. 



SENSORY AND MOTOR INNERVATION OF THE M. CORDIS CAUDALIS 



From an examination of figures 1, 3, 4, and 12 it is evident 

 that the nerve supply for the pulsating muscle for the caudal 

 heart, the M. cordis caudalis, is from certain of the neighboring 

 spinal nerves. It will be seen from these reconstructions that 

 more than one nerve takes part in supplying this muscle, that 

 there is considerable variation in the arrangement and branch- 

 ing of these nerves, resulting in some irregularities in the mode 

 of innervation of the M. cordis caudalis. 



In figure 1 the motor and sensory components of at least 

 five spinal nerves pass between the myotomes and the M. cordis 



