1046 ORGANS OF SPECIAL SENSE 



ning off towards the canthi and towards both borders. Into the superior anterior 

 border of the upper tarsus the lower layer of the levator expansion is attached, con- 

 sisting of smooth muscle-fibres constituting the superior tarsal muscle of Miiller. 

 In like manner, at the inferior border of the lower tarsus, bundles of smooth muscle- 

 fibre are inserted (the inferior tarsal muscle of Miiller), developed in what has 

 been regarded as part of the extension of the sheath of the inferior rectus. 



The palpebral conjunctiva is firmly adherent to the back of the tarsus; but in 

 the orbital part of the lid loose subconjunctival tissue intervenes between it and 

 Miiller's tarsal muscle. Adenoid tissue occurs in the substance of the conjunctiva, 

 especially in its orbital division. Near the upper fornix, the conjunctiva receives 

 expansions of the tendon of the levator palpebrse and of the sheath of the supe- 

 rior rectus, and, at the lower fornix, of the sheath of the inferior rectus. The sur- 

 face of the tarsal conjunctiva shows small elevations or papilla? everywhere; but 

 these are particularly well marked over the attached border of the tarsus. 



Glands of the eyelids. From its manner of formation the eyelid may be re- 

 garded as consisting of two thicknesses of skin, the inner (or posterior) having been 

 doubled back upon the outer at the edge of the lid; thus the cuticle and corium of the 

 skin proper are represented respectively by the conjunctiva and tarsus of the inner 

 thickness. At the free border of the lid, accordingly, we find glands corresponding to 

 the sebaceous and sweat-glands of the skin, viz., large sebaceous glands of the cilia 

 (Zeiss's glands) and the ciliary glands of Moll, which are modified sweat-glands. 

 Again, in the inner skin-thickness of the lid, the tarsal (Meibomian) glands are 

 sebaceous. Acino-tubular mucous glands occur at the attached border of the 

 tarsus (Krause's or Waldeyer's glands), and similar glands also occur at the fornix, 

 and are especially abundant near the outer canthus of the upper lid, close to the 

 efferent ducts of the lachrymal gland; from their structure and the character of 

 their secretion, these acinous or acino-tubular glands have been termed by Henle 

 'accessory lachrymal glands.' Other single tubular glands (Henle), formed 

 merely by the depressions between the papillae, are best developed in the inner and 

 outer fourths of the tarsal conjunctiva of both lids. 



Blood-vessels. The arteries run in the central connective tissue of the lids, 

 mainly in the form of arches near the borders of the tarsus, from which twigs go 

 to the different palpebral tissues. They are supplied by the lachrymal and palpe- 

 bral branches of the ophthalmic, and by small branches derived from the temporal 

 artery. The veins are more numerous and larger than the arteries, and form a 

 close plexus beneath each fornix. They empty themselves into the veins of the 

 face at the inner, and into the orbital veins at the outer, canthus. 



The lymphatic vessels of the lids are numerous, and are principally situated 

 in the conjunctiva. Lymph-spaces also surround the follicles of the tarsal glands. 

 The palpebral lymphatic vessels mainly pass through the parotid nodes; but, some- 

 times at least, those from the inner half of the lower lid go to the submaxillary 

 lymphatic nodes. 



Nerves. (a) Sensory. The upper lid is chiefly supplied by branches of the 

 supraorbital and supratrochlear nerves, the lower lid by one or two branches of 

 the infraorbital. At the inner canthus the infratrochlear nerve also aids in the 

 supply, and, at the outer canthus, the lachrymal. (6) Motor. The palpebral part 

 of the orbicularis is supplied by branches of the facial nerve, which mainly enter 

 it near the outer canthus. Miiller's tarsal muscles are supplied by the sympathetic 

 nervous system. 



The inner palpebral ligament, or tendo oculi, has been referred to previously. 

 Arising from the frontal process of the maxilla, it extends outwards over the front 

 wall of the lachrymal sac, bends round the outer wall of the sac, and then passes 

 backwards to the posterior crest on the lachrymal bone. It is thus U-shaped, 

 having its limbs anterior and posterior, embracing the lachrymal sac; the anterior 

 limb lies immediately beneath the skin, and is visible in the living. The palpebral 

 fibres of the orbicularis are inserted into the outer surface of both limbs, those 

 attached to the posterior limb constituting Horner's muscle. The outer palpe- 

 bral raphe is merely a stronger development of connective tissue in the .orbicu- 

 laris. Both ligaments are connected with the tarsi as already mentioned. 



