57G APPENDIX. 



tissue to, the upper part of the belly of the superior oblique, became 

 blended with the tendon of insertion of that muscle just as it passed 

 under the tendon of insertion of the superior rectus. 



As there are. some slight differences between the arrangements of the 

 oblique muscles of the eyeball of the Equidae and those of Man, it may 

 be necessary to point these out, so as to prevent any misunderstanding 

 as to the position of this small oblique muscle. 



The superior oblique muscle in the horse and ass is 1st, Relatively 

 longer and larger than in man, and is fleshy for some distance after it 

 has passed through the loop, which loop is situated at the base of the 

 orbital process of the frontal bone ; 2nd, The muscle, after passing 

 through the loop, extends almost directly outwards under the tendon 

 of the superior rectus, to gain its insertion between the tendons of 

 insertion of the superior and external recti. The point of insertion is 

 thus not so near to the back of the eyeball as in man. 



The inferior oblique, arising from the lachrymal fossa, is directed 

 forwards and upwards, its belly running in the same direction as the 

 reflected portion of the superior oblique, and becomes finally inserted 

 between the tendons of insertion of the external and inferior recti, much 

 lower down and also farther forwards than in man. 



So far as my researches have gone, this small muscle has not hitherto 

 been described, either in consequence of being an exceptional occurrence 

 in this animal, or of having been overlooked. There can be no doubt, 

 I think, of its being an accessory or check muscle of the superior 

 oblique, placed there for the purpose of preventing the belly of that 

 muscle becoming fixed in the loop through which it has to pass at such 

 an acute angle, in the lower animals more especially. 



Unfortunately, the other eyeball had been removed by one of the 

 students, to whom the subject belonged, before I had commenced my 

 dissections ; but still, on searching within the orbit, I was enabled to 

 find part of the belly and the tendon of origin of a similar muscle, which 

 had precisely the same point of origin, and in all probability, a similar 

 insertion.* 



* (Since the above was published, Dr. Johnston has dissected the muscle in both 

 eyes of two subjects. 1st Edition.) 



