242 Mammalia. 



nerve enters the orbital surface of the muscle, and not the 

 ocular surface, as is generally the case with the other nerves. 

 In close apposition with the Superior Oblique muscle will be 

 seen the most superficial of the muscles of the orbit, viz.^ the 

 Levator Palpehrce Superioris, in contact with the periosteum 

 externally, and the Superior Eectus internally : it will be seen, 

 later on, to arise close to the optic foramen, and may be now 

 traced forwards to its insertion into the forepart of the tarsal 

 cartilage of the eyelid. 



The Fat should be cleaned away round the Superior Oblique 

 muscle, and it will then be seen to be a thin and narrow muscle 

 arising from the outer end of the optic foramen, and passing 

 through a fibrous loop at the upper internal surface of the 

 orbit, before being inserted into the sclerotic coat behind the 

 middle of the eyeball. The pulley, or trochlea, consists of a 

 fibre- cartilaginous ring, attached by fibrous tissue to a 

 small tubercle on the frontal bone at the supero-internal aspect 

 of the orbit. The thin insertion of the muscle passes internal 

 to the superior rectus muscle, and terminates between this 

 and the external rectus. 



The Superior Rectus muscle should be next cleaned out (the 

 upper one of the two just noted), and its origin from the outer 

 margin of the optic foramen, where it is connected with the 

 other recti muscles around the Optic nerve, noted. 



At this point it will be advisable to trace the anterior ter- 

 mination of the Lachrymal and Supra- orbital branches of the 

 Ophthalmic division of the Fifth nerve. The Ophthalmic, the 

 smallest of the three great divisions of the Fifth, is divided in 

 the Sheep into two principal branches : one, the smaller, going 

 towards the back ; the other, the larger, going towards the 

 inner front of the orbit. Of these, the first is made up of two 

 principal factors, vi%., a Lachrymal and Suprarorbital branch ; 

 the second enumerates but one factor, the Nasal branch. The 

 Lachrymal and Supra-orbital branches lie just within the 



