628 MANUAL OF HISTOLOGY. 



passing from behind from the fundus of the bulb, while that from the 

 foremost portion of the choroid, as well as the ciliary body and iris, is 

 also received into them. 



In the iris and ciliary processes numerous frequently anastomosing 

 venous radicles take their rise. Crowded close together, they unite at 

 very acute angles to form larger branches, which reach the choroid after 

 further intercommunication, and diverging here in groups empty them- 

 selves into the adjacent vence vorticosce. Owing to their slender make 

 they may be easily mistaken for arteries. 



The venous vessels of the iris (14) springing from the capillary net- 

 work, and the terminal loops at the edge of the pupil (&), maintain a 

 course similar to that of the arteries ; they lie, however, nearer to the 

 posterior surface than the latter, anastomosing also frequently with one 

 another. 



In their further course back again they communicate either directly 

 with veins of the ciliary processes, or dip into the furrows between the 

 latter, receiving more blood from them, and from the ciliary muscle 

 (15). The processus ciliares are, moreover, drained by a regular venous 

 plexus formed of numerous transverse branches situated within their sub- 

 stance. 



The axial veins, springing from the venae vorticosae of the choroid, 

 pierce the sclerotic at about the equator of the eye -ball to run external 

 to the latter. 



Beside this system of vessels, there is, as has been already remarked, a 

 second venous drainage more anteriorly. The blood from some of the 

 structures lying in the fore part of the eye is carried off, namely, through 

 the anterior ciliary veins (5), and the canal of Schlemm (10) in connec- 

 tion with them, presenting an annular venous plexus (Rouget, Leber). 

 The arrangement of the latter is not, however, by any means the same in 

 all portions of the ring or in different eyes, and its retiform nature may 

 be very slightly marked. Small twigs from the inner part of the scle- 

 rotic, as well as from 12 to 14, somewhat stronger branches from the 

 ciliary muscles (12), open into this ring. The tubes, leaving the canal of 

 Schlemm, named by Leber the plexus venosus ciliaris, are very numerous. 

 They perforate the solera obliquely, opening upon its external surface into 

 a venous plexus, that of the " anterior ciliary veins." 



Having described the vascular supply of the uvea, we shall have but 

 little difficulty with the vessels of the sclerotic. This tunic is fed by the 

 same branches of the ophthalmic artery as the vascular membrane, namely, 

 the art. cil. post, et ant. Their twigs to the sclerotic are seen at (u) and 

 (v). The veins of these two coats are likewise more or less common to 

 both. They empty themselves into the anterior ciliary veins and venae 

 vorticosae. Besides these, however, we have in the posterior part of the 

 sclerotic the small venae ciliares posticae, which, receiving no blood from 

 the choroid, constitute a peculiarity in the vascular arrangement of the 

 fibrous coat. All these vessels, and especially the veins, form a wide- 

 meshed network over the sclerotic. Corresponding to them we find also 

 a similar loose reticulum of capillaries. 



The short posterior ciliary arteries (a, 6), whose distribution to the 

 choroid has been described in the foregoing section, have peculiar and 

 important relations in the neighbourhood of the entrance of the optic 

 nerve into the eye-ball. They are (e) connected, namely, with the 

 vascular supply of the retina (see below), which is otherwise a perfectly 



