60 



THE MYOLOGY OF THE RAVEN. 



47. The rectus internus, after leaving its origin, spreads 

 out over the mesial aspect of the eyeball, clearing by a 

 well-devised arrangement the quadratus and pyramidalis, 

 though in intimate relation with the former : it is finally 

 inserted, in a manner common with the others of the 

 group, upon the sclerotic, or the anterior aspect of the 







J^rvdUr sid<i^ oj ^^^ 



Fig. 23.- 



-The back of the right eye of a Raven, x 2^, and showing tiie cut 

 stumps of the recti and ohliqui muscles, whicli, liowever, are drawn 

 away from the centre to show their proper insertions. The quadratus 

 nictitantis is represented in a state of semi-contraction, when it lifts the 

 tendon of the pyramidalis nictitantis off of the optic nerve. Could 

 the front of this eye now be seen, the mr.mhrana nictitans would be 

 found about three-quarters drawn obliquely across the eye. The pyra- 

 viidalis is here contracting then, and it is evident that both its force 

 and function are augmented by this action of the quadratus. 



The curious elliptical osseous plate surrounding the optic nerve, 

 is also shown in the figure, and I have found it in every Raven's eye 

 that I have dissected. 



eye, or what would be the internal side in the Mammalia. 

 Were it to act alone, the other muscles remaining passive, 

 it would so pull the eyeball as to direct the line of vision 

 to the front. 



By way of recapitulation, then, of the nomenclature of 



