AUTHORS ABf'TRACT OF ^HIS PAPER ISSUEU 

 BY THE BIBLIOGRA.PH1C SERVICE JANUARY 12 



THE HISTORY OF THE EYE MUSCLES 



H. V. NEAL 



Tufts College * 



TWENTY FIGURES 



The muscles which move the eye-ball are a specialized group 

 whose functional importance is quite disproportionate to their 

 size. They are muscles of ancient origin, presumably antedat- 

 ing by millions of years muscles such as tho^e which move the 

 eye-lids. As a result of the investigations of two generations of 

 morphologists we are now in a position to sketch in general 

 outline their probable phylogenesis. The present paper raises 

 the problems — What has been the past history of the eye muscles? 

 What changes have they undergone in their transformation of the 

 fish into the mammal? How many myotomes enter into their for- 

 mation? Are they, like the tongue and appendicular muscles, 

 exotic in origin and derivatives of the post-otic lateral trunk 

 muscles? To what do they owe their present isolation? Can 

 their history be traced back into stages before eyes made their 

 appearance? 



Comparative anatomy has thrown very little light upon th€ 

 history of the eye muscles. Like the eyes with which they are 

 so intimately associated, they appear in the lowest vertebrates 

 in essentially the same form as in man. Indeed their number 

 and their nerve relations are the same in man as in the dogfish. 

 Of the entire group of eye muscles only the superior oblique 

 shows a functional change in the course of phylogeny. The 

 direction of its pull is altered as the result of the development 

 of the trochlear tendon. Comparative anatomy also reveals 

 some aberrations in the innervation of the eye muscles and such 

 curious modifications as in Astroscopus where some of the eye 

 muscles are transformed in to electroplaxes with some striking 

 changes in their innervation. Moreover, in reptiles and some 



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THE JOURNAL OF MORPHOLOGY, VOL. 30, NO. 2 

 MARCH. I'niS 



