[ 3 ° ] 
in fmiling, the Riforius is fufficient of Itfelf; but, 
when great Laughter is promoted, the Buccinator 
takes the whole Action to itfelf, which is begun by 
the former, and pulls the Corner of the Mouth on 
each Side, and ftretchcs the Lips prodigioufly, ac- 
cording to the Degree of Laughter required. 
LIIL 
Of the Quadratus Genx, or Latiifimus Colli. 
Notwithftanding this Mufcle is not among the 
Mufcles of the Lips, we fhall mention it here as a 
Mufcle which belongs partly to the Face. It arifes 
thin, with fome membranous, andfome flefhy Fibres, 
from the Sternum or Breaft-Bone, the Acromion of 
the Scapula, and from the intire Space between them 
occupied by the pectoral and deltoid Mufcles, and 
is inferted partly into the lower Jaw, partly into 
the Buccinator Mufcle, and partly by a thin Mem- 
brane under mod Part of the Skin of the Face. It 
fcrves, according to the Opinion of Dr. 'Douglas? 
to draw the Skin of the Face downwards, and to af- 
fift the Digaftric in opening the Jaws. This laft Of- 
fice is denied by Heiller, and fome others; bur, as 
there is a ftrong Infertion into the lower Jaw of the 
mod confiderable Part of this Mufcle, I cannot but 
join with the former, in the Opinion that its chief 
Office is to open the Jaws: For the Fibres which 
go to the Skin of the Face are very (lender and 
weak ; infomuch that, in many Subjeds, they are 
not to be difeerned at all. As to the Mufcles pro- 
per to the lower Jaw, viz. the Temporalis and Maf- 
