186 DISSECTION OF THE DOG 



band to the zygomatic process of the frontal bone. Its distribution is to the 

 upper eyelid and the adjacent part of the side of the nose. 



M. levator palpebr^e superioris. — The thin, narrow levator muscle of 

 the upper eyelid is dorsal to the eyeball and just underneath the periorbita. 

 Its origin is from the margin of the optic foramen, and its expanded insertion 

 is into the upper eyelid. 



M. obliquus superior. — Of the two oblique muscles of the eye, the more 

 superior arises from the medial side of the optic foramen. Under the zygomatic 

 process of the frontal bone, the fleshy belly of the muscle gives place to a thin 

 rounded tendon, which, playing through a pulley, forms an angle with the rest 



m. obliquus **~ 

 inferior 



. n. infratrochlearis 

 t n. opticus 



t 

 / m. rectus medialis 



n. naso-ciliaris 

 \ y' ,n. trochlearis 



i i ^^ " v n. oculo-motorius. 



! ! Ramus inferior 



m. rectus "■ abductns 



m. rectus lateralis inferior 



Fig. 61. — Dissection of the orbit. 



of the muscle and is attached to the sclera after passing under the tendon of 

 insertion of the superior straight muscle. 



N. trochlearis.— The trochlear or fourth cerebral nerve lies lateral to the 

 superior oblique muscle, which it enters after a very short intraorbital course. 



N. infratrochlearis.— The infratrochlear branch of the ophthalmic 

 nerve may now be examined. The nerve is at first between the medial and 

 superior straight muscles, but later it passes towards the entrance to the orbit 

 between the medial straight and the superior oblique muscles. In order 

 to gain the skin medial to the eye, the infratrochlear nerve passes below the 

 trochlea of the oblique muscle, whence it derives its name. 



N. naso-ciliaris. — The naso-ciliary nerve generally arises from a common 

 stem along with the infratrochlear nerve. In order to reach the ethmoidal 

 foramen, by means of which it leaves the orbit, the nerve turns round the 

 edge of the medial straight muscle and then passes between the medial straight 

 and superior oblique muscles. 



