168 ORBICULARIS PALPEBRARUM. 



ing the orbit and eyelids. It arises from the internal angular process 

 of the frontal bone, from the nasal process of the superior maxillary, 

 and from a short tendon (tendo oculi) which extends between the 

 nasal process of the superior maxillary bone, and the inner extremities 

 of the tarsal cartilages of the eyelids. The fibres encircle the orbit 

 and eyelids, forming a broad and thin muscular plane, which is inserted 

 into the lower border of the tendo oculi and into the nasal process of 

 the superior maxillary bone. Upon the eyelids the fibres are thin 

 and pale, and possess an involuntary action. The tendo oculi, in ad- 

 dition to its insertion into the nasal process of the superior maxillary 

 bone, sends a process inwards which expands over the lachrymal sac, 

 and is attached to the ridge of the lachrymal bone : this is the reflect- 

 ed aponeurosis of the tendo oculi. 



Relations. By its superficial surface it is closely adherent to the 

 integument from which it is separated over the eyelids by a loose 

 areolar tissue. By its deep surface it lies in contact above with the 

 upper border of the orbit, with the corrugator supercilii muscle, and 

 with the frontal and supra-orbital vessels and supra-orbital nerve ; 

 below, with the lachrymal sac, with the origins of the levator labii 

 superioris alseque nasi, levator labii superioris proprius, zygomaticus 

 major and minor muscles, and malar bone ; and externally with the 

 temporal fascia. Upon the eyelids it is in relation with the broad 

 tarsal ligament and tarsal cartilages, and by its upper border gives at- 

 tachment to the occipito-frontalis muscle. 



The CORRUGATOR SUPERCILII is a small narrow and pointed 

 muscle, situated immediately above the orbit and beneath the upper 

 segment of the orbicularis palpebrarum muscle. It arises from the 

 inner extremity of the superciliary ridge, and is inserted into the under 

 surface of the orbicularis palpebrarum at a point corresponding with 

 the middle of the superciliary arch. 



Relations. By its superficial surface, with the pyramidalis nasi, 

 occipito-frontalis and orbicularis palpebrarum muscle ; and by its deep 

 surface, with the supra-orbital vessels and nerve. 



The TENSOR TARSI (Horner's * muscle) is a thin plane of muscular 

 fibres, about three lines in breadth and six in length. It is best dis- 

 sected by separating the eyelids from the eye, and turning them over 

 the nose without disturbing the tendo oculi ; then dissect away the 

 small fold of mucous membrane called plica semilunaris, and some 

 loose cellular tissue under which the muscle is concealed. It arises 

 from the orbital surface of the lachrymal bone, and passing across the 

 lachrymal sac divides into two slips, which are inserted into the 

 lachrymal canals as far as the puncta. 



Actions. The palpebral portion of the orbicularis acts involuntarily 

 in closing the lids, and from the greater curve of the upper lid, upon 

 that principally. The entire muscle acts as a sphincter, drawing at 



* W. E. Horner, M.D. Professor of Anatomy in the University of Pennsyl- 

 vania. The notice of this muscle is contained in a work published in Philadel- 

 phia in 1827, entitled " Lessons in Practical Anatomy." 



