374 JAMES ROLLIN SLONAKER 



posterior portion of the eyeball. This branch gives off some 

 occipital arteries (0) to the semicircular canals and to that por- 

 tion of the head. When the external ophthalmic artery reaches 

 the eye, it divides into three main branches; the superior 

 ophthalmic (OS), the inferior ophthalmic (01), and the ophthal- 

 motemporal (Gp T). These branches will be described later. 



After giving off the external ophthalmic artery the internal 

 carotid turns inward and upward. For some distance it is 

 enclosed in a tube of bone. It soon gives off a branch {cb) which 

 connects the internal carotid to the palatine branch of the ex- 

 ternal carotid. A little farther on it gives off another branch 

 {A) which is directed forward over the ventral surface of the 

 orbit. For a short distance this vessel is also inclosed in a bony 

 tube. In its course this vessel gives off branches to the tissues 

 in this region and finally leaves the orbit at its anterior side. 

 The internal carotid extends inward until it almost meets the 

 internal carotid from the other side, just posterior to the hypo- 

 physis. Here the two carotids are united by a small commis- 

 sural branch {Ac) which extends across in the groove between 

 the floor of the brain and the hypophysis. At this point the 

 carotid makes a sharp turn forward and, after encircling the 

 hypophysis, divides into two branches: the cerebral (C), which 

 runs dorsally to supply the brain ; and the ophthalmic {Ojpl) , which 

 runs parallel with the optic nerve to supply portions of the eye. 



As previously stated, the external ophthalmic artery divides 

 into three branches; two of these, the superior orbital and the 

 inferior orbital, supply the anterior portion of the eyeball, the 

 conjunctiva, and the lids. Figure 13 shows the main distribu- 

 tion of these arteries as seen from the front. 



The inferior orbital artery {01 A) runs forward along the 

 ventral surface of the eye. In its course it gives off numerous 

 branches which supply the skin and the lower portion of the 

 lower lid. Some branches, after supplying the conjunctiva and 

 structures in the inferior fornix, penetrate the sclerotic (c) pos- 

 terior to its union with the cornea. These form the anterior 

 ciliary arteries. The inferior orbital finally leaves the orbit at 

 the anterior lower portion. 



