336 THE MUSCULATURE 



the orbicularis oculi, the corrugator, and the procerus. The orbicularis oculi is a 

 large, flat, elliptical muscle which lies in the eyelids and over the bone surrounding 

 the orbit. Three parts are recognised, a palpebral, an orbital and a lacrimal. 

 The quadrangular corrugator extends from the nasal portion of the frontal bone 

 to the skin of the middle half of the eyebrow; the narrow procerus (pyramidalis 

 nasi) from the bridge of the nose to the skin at the root. The muscles which 

 have an antagonistic action are the levator palpebrse superioris and the epicranius. 

 The levator palpebrse is described in the chapter on the Eye (see Section VIII), 

 the epicranius in the following subsection. 



The orbicularis oculi. — The palpebral portion arises from the ventral surface and margins 

 of the lateral portion of the medial palpebral ligament (tendo oculi), and from the covering of the 

 lacrimal sac. The fibre-bundles spread out as they pass into the eyelids and again are con- 

 centrated toward their insertion into the outer surface of the lateral palpebral ligament. Many 

 of the fibre-bundles interdigitate here without being inserted into the ligament. The muscle 

 in each ej'elid lies between the tarsal plate and the skin, separated from both by loose tissue. 

 The superficial muscle-fibres nearest the margin of the fids constitute the ciliary muscle, or muscle 

 of Riolan. They are very small fibres and probably act on the eyelashes and Meibomian 

 glands. 



The orbital portion arises by a superior origin from the medial palpebral ligament (tendo 

 oculi), the nasal portion of the frontal bone, and the anterior lacrimal crest of the maxilla, and 

 by an inferior origin from the medial palpebral ligament and the medial portion of the inferior 

 rim of the orbit. The fibre-bundles form a flat ring which surrounds the orbit for a consider- 

 able distance, especially inferiorly. The muscle is adherent to the overlying skin. It lies over 

 the bones surrounding the margin of the orbit and over the attachments of several of the facial 

 muscles attached to these bones. With these muscles some of the fibre-bundles are usually 

 continuous. 



The lacrimal portion (tensor tarsi or Horner's muscle) arises from the posterior lacrimal 

 crest of the lacrimal bone and passes down on the dorsal surface of the lacrimal sac and the 

 medial palpebral ligament (tendo oculi). It bifurcates and furnishes a fasciculus attached to 

 each tarsal plate. Some of the fibre-bundles surround the lacrimal canaliculi and some 

 surround the ducts of the tarsal glands and the roots of the eyelashes. 



The corrugator arises from the frontal bone near the fronto-nasal suture. It extends 

 obliquely upward to be inserted into the skin of the middle half of the eyebrow. The fibre- 

 bundles of insertion interdigitate with those of the frontalis. The muscle lies relatively deep. 

 It is covered by the procerus (pyramidalis nasi), the frontalis, and the orbicularis. Under it 

 lie the supra-orbital vessels and nerves. 



The procerus (pyramidalis nasi) overlies the nasal bone. It arises from the lateral cartilage 

 of the nose through a fibrous membrane and also directly from the nasal bone, and is attached 

 to the skin over the root of the nose, where its fibres interdigitate with those of the frontalis. 

 The medial margins of the muscles on each side are more or less fused. 



Nerve-supply. — The muscles of this group are suppUed by temporal and infraorbital branches 

 of the facial nerve which enter the deep surfaces near the lateral margins. 



Action. — The palpebral portion of the orbicularis closes the eyelids, of which the upper 

 moves more freely than the lower. It also serves to dilate the lacrimal sac and allow the 

 tears to flow away readily. The tensor tarsi probably contracts the sac and forces the tears 

 into the nose. The upper half of the orbital portion of the orbicularis contracts and depresses 

 the tissue overhanging the orbit, and stretches the skin of the forehead. The corrugator draws 

 the skin of the brow downward and medially, thus aiding the preceding muscle. It causes the 

 perpendicular furrows characteristic of frowning. The' procerus (pyramidalis nasi) draws down 

 the skin of the forehead and wrinkles the skin across the root of the nose. The lower half of 

 the orbital portion of the orbicularis raises the skin of the cheek, causing the wrinkles seen to 

 radiate from the corner of the eye. The whole set of muscles comes into play in the forcible 

 closure of the eyes. In case of violent expiratory efforts, as in shouting, sneezing, coughing, 

 etc., the eye is thus usually forcibly closed. The pressure thus exerted on the eyeball prevents 

 a too violent flow of blood to the vessels of the eye. Pressure is thought at the same time to 

 be exerted on the lacrimal gland so as to cause the excessive flow of tears often experienced at 

 such times. 



Variations. — The muscles of this group vary in extent and differentiation, and may be more 

 or less fused with one another or with neighbouring muscles. The orbital portion of the or- 

 bicularis, the corrugator, and the procerus have been found absent. 



(/) THE EPICRANIAL MUSCULATURE 

 (Fig. 341) 



The epicranius (o(;('if)ito-frontalis) is formed of the two frontal muscles, which 

 lie on each side of the forehead, the two occipital muscles, which occupy corre- 

 sponding positions on the occipital bone, and of the epicranial aponeurosis, the 

 galea aponeurotica, which extends l)etween these. The occipital muscles arise 

 from tlie supreme nuchal line and are inserted into the galea aponeurotica. The 

 frontal muscles arise from the latter and are inserted into the skin near the eye- 

 brows. The chief function of these muscles is to elevate the brows. The 



