146 ORBITAL GROUP. 



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 cellular tissue which admits of considerable 

 movement. 



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. 



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

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

 section 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 three next groups of 

 muscles will be brought into view. 



2. Orbital group. Orbicularis palpebrarum, 

 Corrugator supercilii, 

 Tensor tarsi. 



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 superior maxillary bone, and the inner ex- 

 tremities of the tarsal cartilages of the eyelids. The fibres encircle 

 the orbit and eyelids, forming a broad and thin muscular plane, 

 which 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 very 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 lachrymal sac, and is attached to the ridge of the lachry- 

 mal bone ; this is the reflected aponeurosis of the tendo oculi. 



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

 integument, from which it is separated over the eyelids by a loose 

 serous cellular 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 labii superioris alaeque nasi, leyator labii superioris proprius, 



