MUSCLES OF THE NECK. 



act from its dorsal margin, assisted by the nasal slip of the occi- 

 pito-frontalis, it will dilate the ala nasi, and has, therefore, been 

 called dilatans nasum by Columbus. 



Orbicularis, or Sphincter Palpebrarum. 



The orbicularis oculi or palpebrarum is a broad circular 

 muscle, lying immediately under the skin of the eyelids, and 

 over the tarsi cartilages. It is much connected with essential 

 points in the anatomy of the eyelid. 



Its diameter exceeds that of the orbit, by from four to eight 

 lines all around. The fixed point of this muscle is principally 

 the ligamentum palpebrale internutn and the internal canthus 

 of the orbit ; for, in the greater part of its extent, besides, it is 

 only loosely attached to the parts below. 



The orbicularis arises, by short tendinous fibres, from the up- 

 per end of the nasal process of the os maxillare superius, from 

 the internal angular process of the os frontis, and from the con- 

 tiguous part of the os unguis. It also arises along the whole 

 superior margin of the internal palpebral ligament. 



The fibres from this origin compose the lamina of the upper 

 eyelid. They may be traced, thence, around to the lower eye- 

 lid, and are found again terminating at the internal canthus of 

 the orbit, where they are fixed into the anterior margin of the 

 orbitar process of the upper maxillary bone, into the corre- 

 sponding ridge of its nasal process, and into the inferior margin 

 of the palpebral ligament. 



The temporal portion of this muscle is attached to the tem- 

 poral fascia, so as to prevent it from being much displaced. It 

 is, therefore, obvious that the effect of the contraction of the 

 upper and of the lower half of the muscle will be to bring the 

 eyelids together. The fulcrum of motion is the internal or na- 

 sal side, as manifested by the radiated wrinkling of the skin at 

 that point. 



The interior portion of this muscle, which is laid upon the 

 tarsi cartilages, is called Ciliaris by Albinus: this distinction, 

 which is too arbitrary, is now abandoned. 



31* 



