842 THE ORGANS OF SPECIAL SENSE. 



nerves, derived from the ciliary, which enter the cornea through the fore part of the sclerotic 

 and form plexuses in the stroma, terminating between the epithelial cells by free ends or in cor- 

 puscles. In cases of glaucoma the ciliary nerves may be pressed upon as they course between 

 the choroid and sclerotic, and the cornea becomes anaesthetic. The sclerotic has very few blood- 

 vessels and nerves. The blood-vessels are derived from the anterior ciliary, and form an open 

 plexus in its substance. As they approach the corneal margin this arrangement is peculiar. 

 Some branches pass through the sclerotic to the ciliary body ; others become superficial and lie 1 

 in the episcleral tissue, and form arches, by anastomosing with each other, some little distance 

 behind the corneal margin. From these arches numerous straight vessels are given off, which 

 run forward to the cornea, forming its marginal plexus. In inflammation of the sclerotic and 

 episcleral tissue these vessels become conspicuous, and form a pinkish zone of straight vessels 

 radiating from the corneal margin, commonly known as the zone of ciliary injection. In inflam- 

 mation of the iris and ciliary body this zone is present, since the sclerotic speedily becomes 

 involved when these structures are inflamed. But in inflammation of the cornea the sclerotic is 

 seldom much affected, though the cornea and sclerotic are structurally continuous. This would 

 appear to be due to the fact that the nutrition of the cornea is derived from a different source 

 from that of the sclerotic. The sclerotic may be ruptured subcutaneously without any laceration of 

 the conjunctiva, and the rupture usually occurs near the corneal margin, where the tunic is thin- 

 nest. It may be complicated with lesions of adjacent parts laceration of the choroid, retina, 

 iris, or suspensory ligament of the lens and is then often attended with haemorrhage into the 

 anterior chamber, which masks the nature of the injury. In some cases the lens has escaped 

 through the rent in the sclerotic, and has been found under the conjunctiva. Wounds of the 

 sclerotic are always dangerous, and are often followed by inflammation, suppuration, and by 

 sympathetic ophthalmia. 



One of the functions of the choroid is to provide nutrition for the retina and to convey ves- 

 sels and nerves to the ciliary body and iris. Inflammation of the choroid is therefore followed 

 by grave disturbance in the nutrition of the retina, and is attended with early interference with 

 vision. In its diseases it bears a considerable analogy to those which affect the skin, and, like it, 

 is one of the places from which melanotic sarcomata may grow. These tumors contain a large 

 amount of pigment in their cells, and grow only from those parts where pigment is naturally 

 present. The choroid may be ruptured without injury to the other tunics, as well as participa- 

 ting in general injuries of the eyeball. In cases of^ uncomplicated rupture the injury is usually 

 at its posterior part, and is the result of a blow on the front of the eye. It is attended by con- 

 siderable haemorrhage, which for a time may obscure vision, but in most cases this is restored as 

 soon as the blood is absorbed. 



The iris is the seat of a malformation, termed coloboma, which consists in a deficiency or 

 cleft, which in a great number of cases is clearly due to an arrest in development. In these cases 

 it is found at the lower aspect, extending directly downward from the pupil, and the gap 

 frequently extends through the choroid to the entrance of the optic nerve. In some rarer cases 

 the gap is found in other parts of the iris, and is then not associated with any deficiency of the 

 choroid. The iris is abundantly supplied with blood-vessels and nerves, and is therefore very 

 prone to become inflamed. And when inflamed, in consequence of the intimate relationship 

 which exists between the vessels of the iris and choroid this latter tunic is very apt to participate 

 in the inflammation. And, in addition, inflammation of adjacent structures, the cornea and 

 sclerotic, is apt to spread into the iris. The iris is covered with epithelium, and partakes of the 

 character of a serous membrane, and, like these structures, is liable to pour out a plastic exuda- 

 tion when inflamed, and contract adhesions, either to the cornea in front (synechia anterior), or 

 to the capsule of the lens behind (synechia posterior). In iritis the lens may become involved, 

 and the condition known as secondary cataract may be set up. Tumors occasionally commence in 

 the iris; of these, cysts, which are usually congenital and sarcomatous tumors, are the 

 most common and require removal. Grummata are not unfrequently found in this situa- 

 tion. In some forms of injury of the eyeball, as the impact of a spent shot, the rebound of a 

 twig, or a blow with a whip, the iris may be detached from the Ciliary muscle, the amount of 

 detachment varying from the slightest degree to the separation of the whole iris from its ciliary 

 connection. 



The retina, with the exception of its pigment-layer and its vessels, is perfectly transparent, 

 so as to be invisible when examined by the ophthalmoscope, so that its diseased conditions are 

 recognized by its loss of transparency. In retinitis, for instance, there is more or less dense and 

 extensive opacity of its structure, and not unfrequently extravasations of blood into its sub- 

 stance. Haemorrhages may also take place into the retina from rupture of a blood-vessel with- 

 out inflammation. 



The retina may become displaced from effusion of serum between it and the choroid or by 

 blows on the eyeball, or may occur without apparent cause in progressive myopia, and in this " 

 case the ophthalmoscope shows an opaque, tremulous cloud. Glioma, a form of sarcoma, and 

 essentially a disease of early life, is occasionally met with in connection with the retina. 



The lens has no blood-vessels, nerves, or connective tissue in its structure, and therefore is 

 not subject to those morbid changes to which tissues containing these structures are liable. It 

 does, however, present certain morbid or abnormal conditions of various kinds. Thus, variations 

 in shape, absence of the whole or a part of the lens, and displacements are amongst its congeni- 

 tal defects. Opacities may occur from injury, senile changes, malnutrition, or errors in growth 

 or development. Senile changes may take place in the lens, impairing its elasticity and render- 



