MUSCLES OF THE TRUNK. 277 



6. Intermediate Posterior Muscle. 



Synonyms.— M-eAins posterior — Bourgelat. (Levator menti — Percivall. Incisive muscle of 

 the lower lip — Leyh.) 



Bourgelat describes, by this name, a small muscular fasciculus, analogous in 

 every respect to the medius anterior. This little muscle takes its origin from the 

 external surface of the body of the lower jaw, beneath the intermediate and 

 corner incisors ; from thence it descends into the texture of the lip, to unite with 

 that of the opposite side on the upper face of the mento-labialis. Several authors 

 have described it as a dependent of the last muscle. 



7. Alveolo-labialis (Buccinator) (Fig. 168, 24). 



Synonyms. — Molaris externus et internus — Bourgelat. {Buccinator — Percivall. Leyh 

 divides this muscle into two portions ; its superficial plane he designates the Buccinator, and 

 the deep plane the Molaris.) 



Preparation. — Proceed to the ablation of the masseter ; dissect the external surface of the 

 muscle, taking care of the risorius Santorini and zygomaticus, which are confounded with it. 

 Then divide it in the middle, as far as the commissure of the lips ; turn down each strip on 

 the jaws, and remove the mucous membrane, in order to study the inner face of the muscle and 

 the attachments of the superficial plane to the maxillary bones. 



Situation — Form. — Situated on the sides of the face, partly concealed by the 

 masseter muscle, and applied to the mucous membrane of the cheeks, the bucci- 

 nator is a flat, thin muscle, elongated in the direction of the head, and formed 

 of two superposed planes. 



Extent — Structure — Attachments. — The deep plane, the longest and least wide, 

 is narrower at its extremities than its middle, and is formed of strongly aponeu- 

 rotic muscular fasciculi, which are attached, posteriorly : 1. To the alveolar 

 tuberosity. 2. To the external surface of the superior maxillary bone, above 

 the last three molar teeth. 3. To the anterior border of the inferior maxillary 

 bone, behind the sixth molar, in common with the depressor labii inferioris. 

 On reaching the commissure of the lips, this muscular layer appears to be 

 continued by small tendon's with the fibres of the orbicularis. 



The superficial plane only begins about the middle of the deep one, the 

 anterior half of which it entirely covers. Its fibres, less tendinous than those of 

 the latter, extend from a median raphe which also divides the deep layer in its 

 length, and are directed, some forwards, some backwards, to terminate in the 

 following manner : the first are inserted into the external face of the super- 

 maxillary bone, above the first molar tooth and the superior interdental space ; 

 the second are attached to the inferior interdental space alone. 



Relations. — Externally, with the masseter, zygomaticus, panniculus, dilator 

 naris lateraUs, levator labii superioris, the parotid duct, which crosses it to enter 

 the mouth, and the facial artery and veins ; internally, with the buccal mucous 

 membrane. The deep plane is accompanied and covered at its anterior border 

 by the upper molar glands ; its posterior border is margined by the inferior molar 

 teeth, which it partially covers. The superficial layer is distinctly separated from 

 the deep one in its anterior part, which is attached to the supermaxillary bone. 

 Behind, these two planes adhere more intimately to one another, though they 

 are found completely isolated by an interstice in which one or two large veins pass. 



Actions. — The function of the buccinator is particularly related to mastication : 

 this muscle, in fact, pushes between the molar teeth the portions of food which 

 fall outside the alveolar arches : but it cannot aid in bringing the two jaws 

 together, as Lecoq has correctly observed. 



