378 JAMES ROLLIN SLONAKER 



branch which, after supplying the superior rectus and the quad- 

 ratus, gives off a small vessel which penetrates the sclerotic just 

 above the optic nerve. After giving off this branch it unites 

 with the main vessel which has almost completely encircled the 

 ©ptic nerve. It then extends forward and unites with a branch 

 from the ophthalmic artery. These anastomoses are, no doubt, 

 of great value in the blood supply to the eye. Owing to the 

 very close fit of the eyeball in the orbit and the short optic 

 nerve, the vessels on one side or the other would be compressed. 

 by the movement of the eyes. In this case a compensatory flow 

 of blood would occur through the vessels not compressed. 



As the ophthalmotemporal artery passes under the external 

 rectus, several branches are given off to the under or bulbar side 

 of this muscle. Two other important branches are given off in 

 this region; one to the pec ten {p) and the other, the long ciliary 

 (Zc). The pectinal artery penetrates the sclera in the angle 

 formed by the sclera and the sheath of the optic nerve. The 

 long ciliary artery pierces the sclera slightly posterior to this. 



On the ventral side of the optic nerve the ophthalmotemporal 

 artery sends branches to the inferior rectus and pyramidalis 

 muscles. A little farther on it divides into three branches, one of 

 which passes under Harder's gland, supplying it with blood, and 

 finally breaks up into small vessels in the inferior oblique. 

 Another branch passes upward, and, after sending a branch to 

 the internal rectus and one which anastamoses with the oph- 

 thalmic, proceeds under the muscle and gland to an oval pig- 

 mented region on the sclera. Here it divides into a number of 

 branches which pierce the sclera as thirteen separate vessels 

 (C and Cc) . The third branch bends around the optic nerve, 

 close to its anterior side, to unite with another of its branches 

 and with the ophthalmic artery. 



When the sclera is removed from the posterior part of the eye 

 the distribution of the arteries which penetrate the outer tunic 

 is seen. Figure 16 shows the larger vessels of the chorioid. 

 At the point where the vessels stop in the figure they penetrate 

 the chorioid and are so covered with pigment that they cannot 

 readily be followed. They, however, spread out and anastomose 



