626 MANUAL OF HISTOLOGY. 



neighbourhood of the ora serrata this peculiar arrangement of vessels is 

 no longer preserved. 



(2.) Turning now to the sources of blood for the anterior portions of 

 the choroidea, the processus ciliares and iris, we find besides the anterior 

 the long posterior ciliary arteries (c). 



These two branches after piercing the sclerotic, and without giving off 

 any twigs, run for a considerable distance over the vascular coat of the 

 eye to the posterior edge of the ciliary muscle. Here each splits into 

 two branches, which penetrate into the ciliary muscle (m\ and parting 

 there from one another bend sideways into arches embracing a correspond- 

 ing portion of the eye-ball. Thus they take part in the construction of a 

 double vascular collar in common with the anterior ciliary arteries to which 

 we must now direct our attention. 



(3.) The anterior ciliary arteries (/), five or six in number, piercing the 

 insertions of the rectic muscles, lie upon the sclera, and running along 

 the latter for a certain distance, eventually perforate it with many branches 

 in the neighbourhood of the ciliary muscle. 



The two vascular circlets, already alluded to, which are derived from 

 both kinds of arteries, are first an anterior, 

 known for a long time past, the circulus 

 arteriosus iridis major (g), which is com- 

 plete, and encircles the outer portion of the 

 iris, but for the most part within the ciliary 

 muscle ; and second, a posterior and external 

 circlet which is incomplete, and imbedded 

 Fig. Hi-Arrangement of the capit- likewise in the same muscle. This may be 

 laries of the choriocapiiiaris of the named the circulus arteriosus musculi cilidris 



(Leber). 



From these two vascular circlets, and partly also immediately from the 

 arterial tubes supplying them, a series of very important branches are 

 given off to different parts of the eye-ball, namely, to the choroid (a), the 

 ciliary muscle (b), the ciliary processes (c), and iris (d). 



(a.) The choroidal twigs (n), variable both as to number and calibre, 

 are connected in the first place with the branches of the posterior short 

 ciliary arteries, and again take part in the formation of the chorio-capil- 

 laris : principally of its anterior portion. 



(b.) The recurrent branches (??i), passing back into the ciliary musde, 

 are very numerous. They are arranged in a very fine network within the 

 latter, and their meshes are disposed according to the direction of its 

 fibres. 



(c.) The arterial twigs to the processus ciliares (I) are very short tubes, 

 sharply curved backwards and inwards. They enter the structures, 

 springing from the circulus arteriosus iridis major, after traversing the 

 ciliary muscle. Each ciliary process then receives either one special twig, 

 or, as is more frequently the case, two or more are supplied to it by one 

 such rootlet. In each process itself the arterial vessels split up rapidly, 

 and subdivide into a considerable number of fine tubes, which form with 

 arches of anastomosis a beautiful and characteristic network. From the 

 latter then spring the venous radicles of the part. 



(d.) The vessels supplying the iris (h) are all derived from the circulus 

 arteriosus iridis major, and extend beyond the outer border of the latter 

 in considerable number. Their direction is more or less towards the 

 anterior surface, and convergent towards the pupil. Giving off lateral 



