Johnston, Nerves of Petromyzonts. 593 



descriptions will not apply to Lampetra. It is much to be desired 

 that some one will undertake a thorough study of the muscles and 

 skeleton of our American species of petromyzonts, both before 

 and after the metamorphosis, by the method of serial sections and 

 reconstructions. 



Motor endings of the trigeminus. — The fibers of the mandibular 

 ramus are coarse in the ganglion, while the motor fibers of the 

 maxillaris can scarcely be distinguished fromthesensory until they 

 reach their muscles. The motor fibers in both maxillaris and 

 mandibularis, how^ever, increase in thickness greatly before they 

 enter their muscles. Many of them are nearly as thick as those of 

 the spinal nerves described above. It is possible in only a few 

 cases to trace out anything like all the branches of one fiber in the 

 muscle, but it is evident in all regions that relatively few fibers 

 enter any given muscle and that each fiber must supply a large 

 number of muscle fibers. In many places enough can be seen of 

 the early divisions of a motor fiber to show that it has a wide dis- 

 tribution and in a few cases some idea can be obtained of the num- 

 ber of end plates supplied by one fiber. In one horizontal section 

 through the tongue muscle one fiber of the mandibular nerve has 

 thirty-nine end plates and in the adjacent section are forty-one 

 more end plates which certainly belong to the same fiber. 



The motor end plates are more highly developed in the buccal 

 and hngual muscles than elsewhere. The muscle fibers in the 

 specialized muscles are smaller and more uniform in diameter than 

 those of the myotomes, and the motor end plate commonly is as 

 long or wide as the width of the muscle fiber. The most common 

 form of end plate is something like that of a horseshoe, although 

 the appearance of a closed ring or network is sometimes given 

 by the free ends of the horseshoe overlapping. Several end plates 

 are drawn at a high magnification in fig. 20, which shows another 

 pecuharity, namely, the arrangement of the end plates in chains. 

 This is by no means uncommon but is perhaps not true of the 

 majority of the endings. There are hundreds of such end plates 

 impregnated in these preparations and in all the specialized 

 muscles they are of the same general form. Sometimes they are 

 reduced to a single knob or two and seldom are they any more 

 complex than the two separate ones shown in fig. 20. 



In the branchial muscles the endings are simpler but are always 

 characteristic enough, I think, to enable one to distinguish between 



