ORBICULARIS PALPEBRARUM 429 



THE MUSCLES OF THE EYELIDS AND EYEBROWS 



These are four in number — viz. the orbicularis palpel^rarum, the tensor tarsi, 

 the corrugator supercilii, and the levator palpeljne superioris. To these may be 

 added a fifth, the frontalis, which has been described. The levator palpebrae 

 superioris will be descril)ed with the or1)ital muscles. The only part of it which is 

 visible in a dissection of the face is its l)road expansion, which is intimately blend(^d 

 with the front of the crescentic plate of condensed fibrous tissue called the upper 

 tarsal cartilage. 



1. ORBICULARIS PALPEBRARUM 



The orbicularis palpebrarum — named from the rounded shape of the majority 

 of its filn'es (orbiculas, a little circle) and its relation to the eyelids — is an oval 

 sheet with a long transverse diameter and so curved as to fit the prominences and 

 depressions of the eyelids and the margin of the orbit. 



It consists of a marginal and a central division: the former stronger and called 

 the orbital portion; the latter thin and pale, and called the palpebral portion. Both 

 have attachments to the tarsal ligaments, by which the so-called tarsal cartilages 

 are fastened to the margins of the orbit. The internal tarsal ligament, or tendo 

 oculi, is a strong flat band of fil^rous tissue al)OUt a sixth of an inch (4 mm.) long 

 with surfaces which look upwards and downwards. It arises from a projection upon 

 the crest of the nasal process of the maxilla, and passes transversely outwards and 

 somewhat upwards in front of the lachrymal sac, to which it gives off an aponeu- 

 rotic covering. It then bifurcates into an upper and a lower division, which diverge 

 to be attached to the inner extremities of the tarsi, here separated by the caruncula 

 lachripnalis. The external tarsal ligament is undivided; it passes from the 

 margin of the frontal process of the malar bone transversely inwards to the ex- 

 tremities of the tarsi, which at the outer commissure of the eyelids are in close 

 contact. 



The orbital portion of the orljicularis palpebrarum consists of a series of con- 

 centric oval 1( )0ps which are attached only at the inner side of the orbit. 



Origin and insertion. — ( 1) The lower part of the internal angular process of 

 the frontal l)one; (2) the posterior half of the outer surface of the nasal process of 

 the maxilla; (3) the upper and lower surfaces of the inner half of the internal 

 tarsal ligament. 



The palpebral portion consists of paler and shorter semielliptical fibres. 



Origin. — The upper and lower surfaces of the outer half of the internal tarsal 

 ligament, together with the adjacent part of the aponeurosis covering the lachrymal 

 sac. 



Insertion. — The upper and lower surfaces of the external tarsal ligament. 



Structure. — Both portions of the muscle are entirely composed of fieshy fibres. 

 In addition to the origin of the orliital portion at the inner part of the orV)it, it gives 

 off processes from its circumference which 1 :)lend with the adjacent muscles, such as 

 the frontalis and the elevator of the upper lip. Moreover, some of the deeper fil)rcs 

 of the muscle decussate with the fibres of those adjacent muscles which lie under 

 cover of the outer loops. 



The innermost fibres of the palpebral portion are shorter than the rest and, 

 instead of extending across the whole length of the tarsi, they terminate upon their 

 free margins, l)etween the attachment of the eyelashes and the orifices of certain 

 glands which line the inner surface of the tarsi. 



Nerve-supply. — The temporal and malar branches of the temporo-facial divi- 

 sion of the facial nerve, which enter the outer part of the muscle upon its deep 

 surface. 



Action. — (1) The orldtal portion l)y its contraction draws the soft parts around 

 the opening of the orbit inwards and towards the palpebral aperture, raising a 

 ridge which deepens the socket of the eye so as to protect the eyeball from injury, 

 e.g. from the blow of a fist; (2) Its upper part will lower the eyebrow, as when 

 the face is exposed to a strong light, or when the mind is wrapt in thought. (3) 



