BRANCHES OF OPHTHALMIC 501 



meseiichynia invaginated the i)riinaiT optic vesicle on its ventral aspect to form the 

 vitreous. Its further description is given in the Anatomy of thk Eye. 



{(1) The Muscular Branxhes 



The muscular branches are very variable in their origin and distril)ution. 

 Tiiey may l)e roughly divided into superior and inferior sets. Tlie superior or 

 smaller set sui)})ly the superior oblique, the levator palpel>ni?, and superior rectus. 

 The interior ])ass forward between the optic nerve and the inferior rectus, supply- 

 ing that nmscle, the internal rectus, and the inferior oblique. From the muscular 

 branches are given ofi' the anterior ciliary arteries. (See Ciliary Arteries.) 



(e) The Ciliary Arteries 



The ciliary arteries are divided into three sets: — The short posterior, the 

 long posterior, and the anterior, (i) The short posterior, five to six in number, 

 come off ehietiy from the ophtlialmic as it is crossing the optic nerve. They run 

 forwards al)out the nerve, dividing into twelve or fifteen small vessels, which per- 

 forate the sclerotic around the entrance of the optic nerve, and are distributed to the 

 choroid coat, (ii) The long posterior ciliary arteries, usually two in number, 

 come off from the ophthalmic on either side of the optic nerve, and run forwards 

 with the short ciliary, to the sclerotic. On piercing the sclerotic, they course for- 

 wards, one on either side in the equatorial line, between that coat and the choroid 

 to the ciliary processes and iris. Their further distril)ution is given under the 

 Anatomy of the Eye. (iii) The anterior ciliary are derived from the muscular 

 branches and from the lachrymal. They run to the globe along the tendons of the 

 recti, forming a zone of radiating vessels beneath the conjunctiva. They perforate 

 the sclerotic about a quarter of an inch (6 mm. ) behind the cornea, and supply 

 the iris and ciliary processes. It is these vessels that are enlarged and congested in 

 iritis, forming the circumcorneal zone of redness so characteristic of that disease. 

 Tliev thtni (lifter from the tortuous vessels of the conjunctiva in that they are 

 straight and }iarallel. 



(/) The Posterior Ethmoidal Artery 



Ine posterior ethmoidal runs inwards between the su])erior oUique and 

 internal rectus, and, leaving the orbit by the posterior ethmoidal canal, together 

 with the s]>heno-ethmoidal branch of the nasal nerve, enters the })Osterior ethmoidal 

 cells, whence it passes through a transverse slit-like aperture Ix'tween the s}»]ienoid 

 bone and cribriform plate of the ethmoid bone into the cranium. It gives oft" < i ) 

 ethmoidal branches to the posterior ethmoidal cells; (ii) meningeal branches 

 to the dura mater lining the crilniform plate; and (iii) nasal branches, which 

 l)ass through the cribriform plate to the superior meatus and ui>i»er si)ongy ])ones 

 of the nose, and anastomose Avith the nasal branches of the si)heno-palatine artery. 



(//) The Anterior Ethmoidal Artery 



The anterior ethmoidal (figs. 339, 387), a larger branch than the posterior 

 ethmoidal, arises in front of the latter, ])asses inwards lietwcen the su])erior o])lique 

 and internal rectus, and, leaving the orl)it through the anterit)r ethmoidal canal, in 

 company with the nasal nerve, enters the cranial cavity. After running a short 

 distance l^eneath the dura mater on the cribriform jilate of the ethmoid bone, it 

 passes into the nose through the horizontal slit-like aperture by the side of the 

 crista galli. Its terminal branch ]>asses along the groove on the under surface of 

 the nasal l)one, and emerges on the nose between the bone and lateral cartilage, 

 terminating in the skin of that organ. It gives off the following branches in its 

 course: — (i) Ethmoidal, to the anterior ethmoidal cells; (ii) meningeal, to the 

 dura mater of the anterior fossa; (iii) nasal, to the middle meatus and anterior 

 part of the nose; (iv) frontal, to the frontal sinuses; (v; cutaneous, or terminal, 

 to the skin of the nose. 



