176 Journal of Comparative Neurology. 



Plate XXII shows the relation of the eye-muscles and the 

 nerves innervating them, to the ophthalmicus profundus or naso- 

 ciliaris trigemini. There are two main lines of descent : on the 

 one hand, by the splitting of the large inferior oblique muscle, 

 a new rectus internus is formed, the earlier muscle of that name 

 disappearing or fusing with the rectus superior ; this gives the 

 condition seen in Petromyzon. On the other hand, the new 

 muscle formed by the split becomes the rectus inferior and the 

 earlier inferior rectus fuses with the rectus internus ; thus arises 

 the proto-urodele type, from which there are three lines of des- 

 cent. One of these lines leads to the selachians, another to 

 the fishes (ganoids and teleosts) and a third to the Amphibia 

 and higher vertebrates. The amphibian branch shows two 

 diverging lines of development, the one leading to Urodeles 

 and the other to Anura, where a new rectus internus is formed 

 and the old one disappears or is fused. 



AlHs remarks in general that "the lines leading to the 

 higher types of each class resemble each other in that the su- 

 perior branch of the oculomotorius in such lines innervates but 

 one of the muscles of the eye, while in the lines leading to the 

 lower types it always innervates tivo." He also says : " There 

 has been but one impulse, if it may be so called, leading to the 

 formation of the arrangements found in higher types and not 

 repeated ones." We may suppose that the splitting of the 

 large inferior oblique muscle spoken of above, is that impulse. 



Allis states that this ancestral tree of the muscles and 

 nerves of the eye-ball are based on "insufficient and perhaps 

 inaccurate data," but it is interesting to note that the same 

 grouping of orders of Ichthyopsida is shown by Hasse and 

 Maurer ; the former basing his conclusions on the study of the 

 development and structure of the vertebral column and the lat- 

 ter on the development of the muscle cells and muscle fibers. 



The innervation of sense organs is discussed at length in 

 this paper, and much of the "review and comparison of nerves" 

 has great interest for those working along these lines. 



Since '88 Allis has discovered that the glossopharyngeal 

 nerve takes no part in the innervation of the canal organs, the 



