1578 A MANUAL OF ANATOMY 



expansions are to be noted. Those which are connected with the external 

 and internal recti are strong, and are attached, respectively, to the orbital 

 process of the malar bone and to the lachrymal crest of the lachrymal bone. 

 The expansion connected with the superior rectus blends with the deep layer 

 of the tendon of the levator palpebrae superioris, and that which is connected 

 with the inferior rectus passes to the inferior tarsal plate. 



The external rectus muscle is to be fully exposed, with the sixth nerve 

 entering its deep or ocular surface. The two heads of the muscle are to be 

 made quite evident, with the following structures passing between them, in 

 order from above downwards : (i) the upper division of the third nerve, 

 (2) the nasal nerve, (3) the lower division of the third nerve, (4) the sixth 

 nerve, and (5) the ophthalmic vein or veins. 



The superior rectus is to be divided and thrown forwards and backwards. 

 On pushing aside and removing a quantity of fat the optic nerve will be 

 exposed, and crossing it from without inwards is the ophthalmic artery. 

 An effort should be made to show the numerous branches of this artery as 

 detailed in the text. The nasal nerve is to be shown crossing the optic nerve 

 from without inwards to the anterior ethmoidal canal, through which it 

 leaves the orbit. The branches of the nerve to be looked for are as follows : 

 (i) the long or sensory root of the ciliary ganglion, which arises from the 

 nasal as it passes between the two heads of the external rectus ; (2) two long 

 ciliary nerves, which communicate with the short ciliary nerves, and accom- 

 pany them ; and (3) the infratrochlear nerve. The latter nerve is given off 

 by the nasal at the anterior ethmoidal foramen, and it is to be followed for- 

 wards to near the pulley of the superior oblique, where it receives a twig 

 from the supratrochlear nerve. Thereafter it passes beneath the pulley, and 

 emerges from the orbit at the inner canthus. The ciliary or lenticular gang- 

 lion will be found on the outer side of the optic nerve. Its long or sensory 

 root will be found coming from the nasal nerve, and its sympathetic root, 

 from the cavernous plexus, usually reaches it through the sensory root. Its 

 short or motor root comes from that branch of the lower division of the third 

 nerve which supplies the inferior oblique muscle. Passing forwards from the 

 ganglion are the short ciliary nerves, which will be seen to range themselves 

 above and below the optic nerve, by which they are conducted to the back 

 part of the sclerotic. The third cranial nerve is to be fully dissected. Its 

 upper and lower divisions are to be shown, and the distribution of their 

 branches made evident, those of the upper division supplying the levator 

 palpebrae superioris and the superior rectus, and those of the lower division 

 supplying the internal rectus, inferior rectus, and inferior oblique. The motor 

 root of the ciliary ganglion comes from the branch to the last-named muscle. 

 The dissector is to note that the branches of the third nerve enter the muscles 

 which they supply on their deep or ocular surface, except in the case of the 

 branch to the inferior oblique, which enters the posterior border of that muscle. 



In connection with the origins of the recti muscles the fibrous ring in the 

 region of the optic foramen is to be examined ; and its upper part, or superior 

 tendon of Lockwood, and lower part, or ligament of Zinn, are to be 

 noted. 



The inferior oblique muscle is situated below the eyeball and also on its 

 outer aspect. In order to expose this muscle the lower eyelid is to be everted, 

 and the conjunctiva divided along the inferior fornix or line of reflection from 

 the lower eyelid on to the eyeball. The origin of the muscle will be found at 

 the anterior and inner part of the floor of the orbit, immediately external to 

 the opening of the lachrymal canal. 



The orbital or temporo-malar nerve, which enters the orbit through the 

 spheno-maxillary fissure, is to be looked for in two divisions — temporal and 

 malar. The temporal branch receives a communicating twig from the 

 lachrymal nerve, and ascends upon the outer wall of the orbit to the temporal 

 canal. The malar branch passes forwards in the angle between the outer 

 wall and floor to the malar canal. 



During the dissection of the orbit the ophthalmic artery and its branches, 

 as well as the ophthalmic vein or veins, are to be kept in view. 



