430 



THE MUSCLES 



The palpebral portion will lower the vipper and raise the lower eyelid, in elosiire of 

 the eye. (4) The hrni eontraction of the Avhole nmsele presses upon the eyeball, 

 and supports it from the evil elfeet of a strong expiratory effort, which by the rush 

 of blood int(5 the interior of the eyeliall might burst its thin-walled vessels, and do 

 serious harm to the delicate structures within. Thus it will l)e noticed that in 

 shouting, sneezing, or violent coughing the eyes are tightly closed. (5) By pressure 

 upon the lachrymal gland it is probable that the nmsele influences the secretion of 

 tears: hence their flow during violent coughing or laughter. It wull also draAv out- 

 wards and forwards the covering of the lachrymal sac, and so produce a suction of 

 the tears through the canaliculi into the sac. 



Relations. — Superficially, the skin; upon its deep surface the tarsal cartilages 

 and thfir ligaments, the palpe])ral ligaments and the expansion of the tendon of 

 the levator palpebrse superioris; the liones which bound the opening of the orbit, 

 the frontalis and corrugator supercilii muscles aljove; the temporal fascia exter- 

 nally; tlie zygomaticus minor, levator labii superioris, and levator labii superioris 

 alaeque nasi, below; also the supraorbital vessels and nerve, the supratrochlear 

 nerve, the terminal portion of the facial artery, and the palpebral branches of the 

 infraorbital vessels and nerve. 



2. TENSOR TARSI 



The tensor tarsi — named from its supposed action upon the tarsus — is a small 

 muscle com}»osed of two flat slips, which are closely connected with the preceding 

 muscle. 



Fig. 310. — The Texsor Tarsi and Corrugator Supercilii. 



Orbicularis 

 palpebrarum 



Tensor tarsi 



Corrugator supercilii 

 Obliquus superior 



Obllquus inferior 



Origin. — The crest of the lachrymal bone. 



Insertion. — The posterior aspect of the inner end of the tarsi. 



Structure. — Arising as a thin muscular sheet, at the back of, and in close con- 

 tact with, the outer surface of the lachrymal sac, the muscle divides into tAvo slips 

 which run behind the canaliculi, and are inserted into the edge of the eyelids near 

 the puncta lachrymalia. 



Nerve-supply. — From the infraorbital branch of the upper division of the 

 facial nerve, by small slips which enter the muscle near its lower Ijorder. 



Action. — To compress the lachrymal sac l:)y drawing inwards and l^ackwardstho 

 outer ])ai-t of the tendo oculi and the inner ends of the tarsi. 



Relations. — Internally and in front, the lachrymal sac; externally and lu'hind, 

 the orbital fat from which it is separated by the capsule of Tenon. 



3. CORRUGATOR SUPERCILII 



The corrugator supercilii — named from its action, the Avrinkling of the brow — 

 is a short ribbon-:-ha])cd muscle. 



Origin. — The inner extremity of the superciliary ridge of the frontal bone. 



