824 THE ORGANS OF SPECIAL SENSE. 



Epistaxis is a very common affection in children. It is rarely of much consequence, and 

 will almost always subside, but in the more violent haemorrhages of later life it may be 

 necessary to plug the posterior nares. In performing this operation it is desirable to remember 

 the size of the posterior nares. A ready method of regulating the size of the plug to fit 

 the opening is to make it of the same size as the terminal phalanx of the thumb of the patient 

 to be operated on. 



Nasal polypus is a very common disease, and presents itself in three forms : the gelatinous, 

 the fibrous, and the malignant. The first is by far the most common. It grows from the 

 mucous membrane of the outer wall of the nasal fossa, where there is an abundant layer of 

 highly vascular submucous tissue; rarely from the septum, where the mucous membrane is 

 closely adherent to the cartilage and bone, without the intervention of much, if any, submucous 

 tissue. Their most common seat is probably the middle turbinated bone. The fibrous polypus 

 generally grows from the base of the skull behind the posterior nares or from the roof of the nasal 

 fossae. The malignant polypi, both sarcomatous or carcinomatous, may arise in the nasal cavities 

 and the naso-pharynx ; or they may originate in the antrum, and protrude through its inner wall 

 into the nasal fossa. 



Rhinoliths, or nose-stones, may sometimes be found in the nasal cavities, from the formation 

 of phosphate of lime upon either a foreign body or a piece of inspissated secretion. 



THE EYE. 



The eyeball is contained in the cavity of the orbit. In this situation it is 

 securely protected from injury, whilst its position is such as to ensure the most 

 extensive range of sight. It is acted upon by numerous muscles, by which it is 

 capable of being directed to different parts ; it is supplied by vessels and nerves, 

 and is additionally protected in front by several appendages, such as the eyebrow, 

 eyelids, etc. 



The eyeball is imbedded in the fat of the orbit, but is surrounded by a thin 

 membranous sac, the capsule of Tenon, which isolates it, so as to allow of free 

 movement. 



The capsule of Tenon consists of a thin membrane which envelops the eyeball 

 from the optic nerve to the ciliary region, separating it from the orbital fat and 

 forming a socket in which it plays. Its inner surface is smooth, and is in contact 

 with the outer surface of the sclerotic, the perisclerotic lymph-space only interven- 

 ing. This lymph-space is continuous with the subdural and subarachnoid spaces, 

 and is traversed by delicate bands of connective tissue which extend between the 

 capsule and the sclerotic. The capsule is perforated behind by the ciliary vessels 

 arid nerves and by the optic nerve, being continuous with the sheath of the latter. 

 In front it blends with the ocular conjunctiva, and with it is attached to the ciliary 

 region of the eyeball. It is perforated by the muscles which move the eyeball and 

 on each it sends a tubular sheath. The sheath of the Superior oblique is carried 

 as far as the fibrous pulley of that muscle ; that on the Inferior oblique reaches as 

 far as the floor of the orbit, to which it gives off a slip. The sheaths on the recti 

 are gradually lost in the perimysium, but they give off important expansions. 

 The expansion from the Superior rectus blends with the tendon of the Levator 

 palpebrae ; that of the Inferior rectus is attached to the inferior tarsal plate. 

 These two recti, therefore, will exercise some influence on the movements of the 

 eyelids. The expansions from the sheaths of the Internal and External recti are 

 strong, especially the one from the latter muscle, and are attached to the lachrymal 

 and malar bones respectively. As they probably check the action of these two 

 recti, they have been named the internal and external check ligaments. 



Lockwood has also described a thickening of the lower part of the capsule of 

 Tenon, which he has named the suspensory ligament of the eye. It is slung like a 

 hammock below the eyeball, being expanded in the centre and narrow at its 

 extremities, which are attached to the malar and lachrymal bones respectively. 1 



The eyeball is composed of segments of two spheres of different sizes. The 

 anterior segment is one of a small sphere, and forms about one-sixth of the eyeball. 

 It is more prominent than the posterior segment, which is one of a much larger 

 sphere, and forms about five-sixths of the globe. The segment of the larger sphere 



^See a paper by C. B. Lockwood, Journal of Anatomy and Physiology, vol. XL, part i., p. 1. 



