ARTERIES AND MUSCLES OF THE ORBIT. 31 



brain. As it winds through the cavernous sinus it is sur- 

 rounded by nervous plexuses derived from the sympathetic 

 nerve of the neck ; the branches of these plexuses are very 

 minute, and in an injected subject are not likely to be 

 found ; they are called the carotid and cavernous plexuses, 

 the former being on the outer side at the entrance of the 

 sinus, and the latter close to the root of the anterior clinoid 

 process, which should be cut away to examine it. 



ARTERIES AND MUSCLES OF THE DRBIT. 



In order to examine the ophthalmic artery and other contents of 

 the orbit, the frontal bone should be sawed down to the orbit at its 

 inner as well as at its outer angle, and the two incisions continued 

 backward with a chisel till they meet near the optic foramen ; the 

 bone being turned down over the eye, but not removed, the orbit is 

 exposed, filled with a soft delicate fat. The muscles and arteries 

 require patience for their dissection ; these may be dissected upon one 

 side, and the nerves upon the other. The eye of any large animal, 

 if removed with all the contents of the orbit, permits the verification, 

 on a larger scale 3 of many of the points about to be described. 



The ophthalmic artery enters the orbit at the optic fora- 

 men on the outer side of the optic nerve ; it gives off 

 numerous small branches not always reached by the injec- 

 tion. Its first branch is the lachrymal; this lies along the 

 upper border of the external rectus muscle, in company 

 with the lachrymal nerve ; it is distributed to the lachrymal 

 gland and eyelids. The supra-orbital branch rests upon the 

 levator palpebrse muscle, and passes forward through the 

 supra-orbital foramen, where it divides upon the forehead, 

 and is distributed to the muscles and integument. The 

 ethmoidal branches, two in number, pass through the eth- 

 moiclal foramina, and are distributed to the dura mater 

 and nasal fossae. The palpebral are given oft' by a common 

 trunk which divides into two branches near the inner angle 

 of the C3'elids, to which they are distributed. The frontal 

 branch emerges at the inner angle of the eye, and is dis- 

 tributed to the forehead. The nasal also emerges at the 

 inner angle, and divides into two branches, one of which 

 anastomoses with the angular or terminal branch "of the 

 facial, and the other under the name of the dorsalis nasi is 

 distributed to the nose. The muscular branches supply 

 the muscles, and give off some small twigs to the eyeball, 

 called anterior ciliary. The short ciliary branches enter 

 the eyeball around the optic nerve ; two of these, one on 

 each side, piercing the sclerotic, farther forward, are called 



