NASAL GROUP. 179 



n rotatory movement upon the eyeball ; and in animals provided with a 

 retractor muscle, they also act as antagonists to its action. 



Actions. The levator palpebraB raises the upper eyelid, llie four recti, 

 acting singly, pull the eyeball in the four directions ; upwards, downwards, 

 inwards, and outwards. Acting by pairs, they carry the eyeball in the 

 diagonal of these directions, viz. upwards and inwards, upwards and out- 

 wards, downwards and inwards, or downwards and outwards. Acting all 

 together, they directly retract the globe within the orbit. The superior 

 oblique muscle, acting alone, rolls the globe inwards and forwards, and 

 carries the pupil outwards and downwards to the lower and outer angle 

 of the orbit. The inferior oblique, acting alone, rolls the globe outwards 

 and backwards, and carries the pupil outwards and upwards to the upper 

 and outer angle of the eye. Both muscles acting together, draw the eye- 

 ball forwards, and give the pupil that slight degree of eversion which en- 

 ables it to admit the largest field of vision. 



4. Nasal Group. Pyramidalis nasi, 

 Compressor nasi, 

 Dilatator naris. 



The PYRAMIDALIS NASI is a small pyramidal slip of muscular fibres sent 

 downwards upon the bridge of the nose by the occipito-frontalis. It is 

 inserted into the tendinous expansion of the compressores nasi. 



Relations. By its upper surface with the integument ; by its under sur- 

 face with the periosteum of the frontal and nasal bone. Its outer border 

 corresponds with the edge of the orbicularis palpebrarum, and its inner 

 border with its fellow, from which it is separated by a slight interval. 



The COMPRESSOR NASI is a thin and triangular muscle ; it arises by its 

 apex from the canine fossa of the superior maxillary bone, and spreads out 

 upon the side of the nose into a thin tendinous expansion, which is con- 

 tinuous across its ridge with the muscle of the opposite side. 



Relations. By its superficial surface with the levator labii superioris 

 proprius, the levator labii superioris alaeque nasi, and the integument ; by 

 its deep surface with the superior maxillary and nasal bone, and with the 

 alar and lateral cartilages of the nose. 



The DILATATOR NARIS is a thin and indistinct muscular apparatus ex- 

 panded upon the ala of the nostril, and consisting of an anterior and a 

 posterior slip. The anterior slip (levator proprius alse na^si anterior) ex- 

 tends between the lateral and alar cartilage at about midway betw r een the 

 tip and the attached margin of the nose. The posterior slip (levator pro- 

 prius alse nasi posterior) is attached above to the margin of the nasal pro- 

 cess of the superior maxillary bone, and below to the small cartilages of 

 the ala nasi. These muscles are difficult of dissection from the close 

 adherence of the integument to the nasal cartilages. 



Actions. The pyramidalis nasi, as a point of attachment of the occi- 

 pito-frontalis, assists that muscle in its action : it also draws down the 

 inner angle of the eyebrow, and by its insertion fixes the aponeurosis of 

 the compressores nasi. The compressores nasi appear to act in expanding 

 rather than in compressing the nares ; hence probably the compressed 

 state of the nares from paralysis of these muscles in the last moments of 

 life, or in compression of the brain. The use of the dilatator naris is ex 

 pressed in its name. 



