Kingsbury, Oblongata in Fishes. 23 



bles that in Amia and the correctness of the homology seems 

 probable. 



An estimate of the absolute amount of development these 

 systems have undergone in the Eventognathi and the extent to 

 which it alone has influenced the morphology of the oblongata 

 appears as yet impossible, because all the necessary data are not 

 known. A simple concentration of structure whether due to 

 intrinsic or extrinsic causes, might in some cases appear as a 

 greater development. The fusions, also, are unexplainable until 

 a study of the development of the oblongata has been made in 

 which are carefully considered the conditions of growth and the 

 relation of the oblong-ata to the cranial wall and ear. 



Conclusion. 



To sum up, then, the result of the foregoing observations, 

 the morphologically dorsal region of the oblongata is composed 

 of three systems, the spinal Vth tract, the fasciculus communis 

 system and the acusticum. The first is the direct representa- 

 tive in the oblongata of the dorsal horn and associated columns 

 of alba of the myel ; the other two regions appear peculiar to 

 the oblongata, the first typically more mesal, the second dorsal 

 and capped by a caudal extension of the molecular layer of the 

 cerebellum. The spinal V furnishes all (?) the sensory fibers 

 of the trigeminal nerve and, in Amia, Perca, Amiums, Roccus and 

 Lepomis, at least, a small contingent of fibers to the Xth (possi- 

 bly in Ganoids (y^wz"^), to the seventh also). From \}i\Q fascicu- 

 lus communis spring the larger part of the ganglionated IX and 

 X and VII ; while from the tuberculum acusticum, the nerves 

 supplying the ear and the organs of the lateral line system. In 

 Amia, and it is probably so for other Ganoids, the spinal V is 

 superficial, in other words the acusticum is wholly dorsal. In 

 Teleosts the acusticum also extends laterad covering and sub- 

 merging to a greater or less extent the spinal fifth tract. The 

 first condition, that in Amia, is evidently the simpler. In Uro- 

 deles and Petromyzon (Ahlborn) the spinal (ascending) V occu- 

 pies a superficial position. The results of His and Minot on 



