102 EDWARD PHELPS ALLIS, JUN. 



lying relatively close together near the middle line of the top 

 of the head. This position of these pores seems a singular one, 

 if each endolymphatic duct represents the persistent, primary 

 communication of the ear capsule with the exterior, and if 

 the ear capsule itself represents a section of the main infra- 

 orbital sensory line that has been cut out between the facialis 

 and glossopharyngeal sections of that line, and enclosed 

 exactly as the short separate sections of the lateral canals 

 are. The position of the pore, and its long tube, would seem 

 to be much more easily explained on the assumption that the 

 ear, if it be developed from an organ of the main infra-orbital 

 lateral line, had been developed after the manner of the 

 ampullae rather than after the manner of the lateral canals. 



There were, in the half of the supratemporal commissure, in 

 the specimen examined in sections, eleven sense organs and 

 twelve primary tubules. Whether these tubules were all 

 arranged one between each two successive organs could not 

 be definitely determined, but such was probably the case. The 

 mesial tubule was not median in position, and there was no 

 sense organ apparent between it and the mesial tubule of the 

 opposite side. In the dissected specimen from which the 

 drawings were made there were but eight tubules in the one 

 half of the entire commissure, the mesial one not being median 

 in position. The tubules all run directly backward from the 

 commissure. 



The organs of the commissure are all innervated by 

 branches of a large nerve that arises from the nervus 

 linese lateralis while that nerve is still traversing the canal 

 by which it issues, with the nervus vagus, from the cranial 

 cavity. This supratemporal branch of the nervus linetB late- 

 ralis runs upward from the nervus, through a special canal in 

 the cartilage of the skull, and issues on the dorsal surface 

 of the skull posterior to the commissure and internal to the 

 cranial extension of the- trunk muscles. There it turns 

 forward, and passing internal to and beyond the commissure 

 reaches the anterior edge of the trunk muscles. There it 

 turns backward superficial to those muscles, and breaking 



