ORBITAL GROUP. 167 



This dissection requires care ; for the muscle is very thin, and without 

 attention would be raised with the integument. There is no deep 

 fascia on the face and head, nor is it required ; for here the muscles are 

 closely applied against the bones upon which they depend for support, 

 whilst in the extremities the support is derived from the dense layer 

 of fascia by which they are invested, and which forms for each a dis- 

 tinct sheath. 



The OCCIPITO-FRONTALIS is a broad musculo-aponeurotic layer, 

 which covers the whole of the side of the vertex of the skull, from the 

 occiput to the eyebrow. It arises by tendinous fibres from the outer 

 two-thirds of the superior curved line of the occipital, and from the 

 mastoid portion of the temporal bone. Its insertion takes place by 

 means of the blending of the fibres of its anterior portion with those 

 of the orbicularis palpebrarum, corrugator supercilii, levator labii supe- 

 rioris alaeque nasi, and pyramidalis nasi. The muscle is fleshy in 

 front over the frontal bone and behind over the occipital, the two por- 

 tions being connected by a broad aponeurosis. The two muscles 

 together with their aponeurosis cover the whole of the vertex of the 

 skull, hence their designation galea capitis ; they are loosely adherent 

 to the pericranium, but very closely to the integument, particularly 

 over the forehead. 



Relations. This muscle is in relation by its external surface from 

 before backwards, with the frontal and supra-orbital vessels, the 

 supra-orbital and facial nerve, the temporal vessels and nerve, the 

 occipital vessels and nerves, and with the integument, to which it 

 is very closely adherent. Its under surface is attached to the peri- 

 cranium by a loose areolar tissue which admits of considerable move- 

 ment. 



Action. 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 palpebramm, 

 Corrugator supercilii, 

 Tensor tarsi. 



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

 tinuing the longitudinal incision of the vertex of the previous dissec- 

 tion 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 superfi- 

 cial fascia carefully from the whole of the region included by these 

 incisions, and the present with the two following groups of muscles 

 will be brought into view. 



The ORBICULARIS PALPEBRARUM is a sphincter muscle, surround- 



