176 



OCULAR GROUP. 



Fig. lOG.f 



The TENSOR TARSI (Homer's* muscle) is a thin plane of musculai 

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



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 sur- 

 face of the lachrymal bone, and passing 

 across the lachrymal sac divides into two 

 slips, w r hich are inserted into the lachry- 

 mal 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 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 fore- 

 head. The tensor tarsi, or lachrymal muscle, draws the extremities of 

 the lachrymal canals inwards, so as to place the puncta in the best posi- 

 tion 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. Hor- 

 ner is acquainted with tw^o persons who have the voluntary power of 

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

 angle of the eye. 



3. Ocular group. Levator palpebra?, 

 Rectus superior, 

 Rectus inferior, 

 Rectus internus, 

 Rectus externus, 

 Obliquus superior, 

 Obliquus inferior. 



Fig. 1074 



Dissection. To open the orbit (the 

 calvarium and brain having been re- 

 moved) the frontal bone must be sawn 

 through at the inner extremity of the 

 orbital ridge, and, externally, at its 

 outer extremity. The roof of the or- 

 bit may then be comminuted by a few 

 light blows with the hammer ; a pro- 

 cess easily accomplished, on account 

 of the thinness of the orbital plate of 

 the frontal bone and lesser wing of the 



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

 notice of this muscle is contained in a work published in Philadelphia in 1827, entitled 

 * Lessons in Practical Anatomy/' 



j-A view of the tensor tarsi muscle. 1, 1. Bony margins of the orbit. 2. Opening 

 Letween the eyelids. 3. Internal face of the orbit. 4. Origin of the tensor tarsi. 5, 5. 

 Insertion into the neighbourhood of the puncta lachrymalis. 



i The muscles of the eyeball ; the view is taken from the outer side of th-e right orbit. 

 j. A small fragment of the sphenoid bone around the entrance of the optic nerve into 

 th orbit. 2. The optic nerve. 3. The globe of the eye. 4. The levator palpebrse 



