ORBITAL GROUP. 175 



nerves, and with the integument, to which it is very closely adherent. Its 

 under surface is attached to the pericranium by a loose areolar tissue 

 which admits of considerable movement. 



Actions. To raise the eyebrows, thereby throwing the integument of 

 the forehead into transverse wrinkles. Some persons have the power of 

 moving the entire scalp upon the pericranium by means of these muscles. 



2. Orbital group. Orbicularis palpebrarum, 

 Corrugator supercilii, 

 Tensor tarsi. 



Dissection. The dissection of the face is to be effected by continuing 

 the longitudinal incision of the vertex of the previous dissection onwards 

 to the tip of the nose, and thence downwards to the margin of the upper 

 lip ; then carry an incision along the margin of the lip to the angle of the 

 mouth, and transversely across the face to the angle of the lower jaw. 

 Lastly, divide the integument in front of the external ear upwards to the 

 transverse incision which was made for exposing the occipito-frontalis. 

 Dissect the integument and superficial fascia carefully from the whole of 

 the region included by these incisions, and the present with the two fol- 

 lowing groups of muscles will be brought into view. 



The ORBICULARIS PALPEBRARUM is a sphincter muscle, surrounding 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 supe- 

 rior 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, wliich 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 addition to its insertion into the nasal process of the 

 superior maxillary bone, sends a process inwards which expands over the 

 .achrymal sac, and is attached to the ridge of the lachrymal bone : this is 

 the reflected aponeurosis of the tendo oculi. 



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

 ment 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 alaBque 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 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 extremity 

 of the superciliary ridge, and is inserted into the under surface of the orbi- 

 cularis palpebrarum at a point corresponding with the middle of the super- 

 ciliary arch. 



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

 frontalis and orbicularis palpebrarum muscle ; and by its deep surface* 

 \vith the supra-orbital vessels and nerve. 



