204 THE HEAD AND NECK 



the Conjunctiva, which is reflected from them on to the anterior 

 surface of the eyeball. The lines along which this reflection 

 takes place are termed the superior and inferior fornices of the 

 conjunctiva. Where it covers the cornea, the conjunctiva is 

 represented by a translucent layer of stratified epithelium. 

 The upper eyelid may be everted along the upper border of the 

 tarsus, and in this way the conjunctiva on its surface may be 

 exposed for the purpose of removing foreign bodies. E version 

 of the lid brings into view the tarsal or Meibomian glands, which 

 appear as yellow streaks near its free margin. It is therefore 

 from this surface that tarsal cysts, which are simply obstructed 

 tarsal glands, are excised. The sensory nerves of the conjunctiva 

 are all derived from the trigeminal (mainly supra-orbital 

 and infra-orbital branches). Blepharo-spasm and lacrimation 

 may be caused reflexly by the presence of foreign bodies or 

 by an inflammatory condition of the conjunctival sac. In 

 paralysis of the trigeminal, conjunctivitis or corneal ulceration 

 frequently results from the presence of particles of dirt, which 

 are unrecognised owing to the loss of sensibility. Ultimately, 

 the intra-ocular structures become affected and pan-ophthalmitis 

 ensues. 



The arterial supply of the lids is derived from the ophthalmic 

 artery. The corresponding veins communicate with the oph- 

 thalmic veins, which join the cavernous sinus, and also with the 

 superficial temporal and anterior facial veins. On account of 

 the existence of this double channel of return, effusions into the 

 eyelids are absorbed with great rapidity. Both lids contain 

 a rich network of lymph vessels, and, as a result, drugs placed in 

 the conjunctival sac, in the form of lamellae, are quickly absorbed. 

 From the lateral half of the lids the lymph vessels pass to the 

 anterior auricular lymph gland, while those from the medial 

 half follow the course of the anterior facial vein, and pass through 

 the facial lymph glands, before terminating in the submaxillary 

 lymph glands. 



The tarsi are connected to the upper and lower margins of 

 the orbit by fibrous tissue, which forms a sheet sufficiently strong 

 to delay a retro-tarsal haemorrhage from passing forwards into 

 the subcutaneous tissue of the eyelid. In fracture of the skull 

 involving the roof of the orbit, vthe haemorrhage appears first 

 under the margins of the conjunctiva, and then spreads in a 

 fan-shaped manner towards the cornea. The blood remains 

 red owing to the thinness of the conjunctiva and the consequent 



