OCULAR GROUP. 147 



zygomaticus major and minor muscles, and malar bone ; and exter- 

 nally with the temporal fascia. Upon the eyelid it is in relation 

 with the broad tarsal ligament and tarsal cartilages, and by its upper 

 border gives attachment 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 ex- 

 tremity of the superciliary ridge and is inserted into the under 

 surface of the orbicularis palpebrarum. 



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 (Homer'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 of 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 involun- 

 tarily 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 the same time, by means of its osseous attachment, the 

 integument and lids inwards towards the nose. The corrugatores 

 superciliorum draw the eyebrows downwards and inwards, and 

 produce the vertical wrinkles of the forehead. The tensor tarsi, or 

 lachrymal muscle, draws the extremities of the lachrymal canals 

 inwards, so as to place the puncta in the best position for receiving 

 the tears. It serves also to keep the lids in relation with the surface 

 of the eye, and compresses the lachrymal sac. Dr. Horner is ac- 

 quainted with two persons who have the voluntary power of draw- 

 ing the lids inwards by these muscles so as to bury the puncta in 

 the angle of the eye. 



3. Ocular group. Levator palpebrae, 

 Rectus superior, 

 Rectus inferior, 

 Rectus internus, 

 Rectus externus. 

 Obliquus superior, 

 Obliquus inferior. 



Dissection. To open the orbit (the calvarium and brain having 

 been removed) the frontal bone must be sawn through at the inner 

 extremity of the orbital ridge ; and, externally, at its outer extremity. 



* W. E. Homer, M.D., Professor of Anatomy in the University of Pennsylvania. 

 The notice of this discovery is contained in a work published in Philadelphia in 1827, 

 entitled " Lessons in Practical Anatomy." 



