t s an energec eevaor o e ower p. 



.i dissect this muscle, the directions given for the preparation >f the anterior medium 

 MiHice. 



MUSCLES OF Till- JIEAD. 223 



It is an energetic elevator of the lower lip. 



will 



B. Mafseteric -or Temporo-maxillary Region. 



This pair region comprises five muscles lor the movement of the lower 

 jti\v. These are : the ma6*eter, temporal, internal pterygoid, external pterygoid, 



and i1iijniili-i<-n#. 



,nration.\. First study the digastricua and its stylo-maxillnry portion, with the 

 internal pterygoid, in preparing the hyoid muscles as they are represented in fig. 111. 

 J. Kxpoae the pterygoideus i xt. rnus, by removing in this preparation the hyoid bone and 

 its <1. i n.lriH'i s, as well as the two preceding muscles. 3. To dissect the temporal!*, 

 excise tin- exd rnal pteryu'oitlrus I'mm its inferior bonier, an operation which exposes the 

 orbital tWiculus of the temporalia; then turn over the piece, saw oti' the orbital process 

 at each e:nl. and remove the eye and auricular muscles. 4. Dissect the masseter in 

 clearing away from its external surface the cuticularis and the vessels and nerves which 

 i it. 



1. Masseter. (Fig. 110, 23.) 

 Synonyms. Zygomatico-maxillaris Girard. ^The zygomatico maxillaris of Leyh.) 



at inn Form Structure. Applied against the external face of the 

 lo WIT jaw, the masseter is a short, wide, and very thick muscle, flattened on 

 both sides, irregularly quadrilateral, and formed of several superposed planes, 

 two of which are perfectly distinct towards the temporo-maxillary articula- 

 tion, by the somewhat different direction of their fibres. These are divided 

 by a considerable number of intersections, and are covered by a strong 

 aponeurotic layer, which becomes gradually thinner backwards and down- 

 wards. 



Attachments. The fasciculi of the masseter have their fixed insertion on 

 the zygomatic crest. Their movable insertion is on the imprints which 

 cover the upper half of the inferior maxillary branch. 



Relation*. It responds, by its superficial face, to the facial portion of 

 cuticularis colli, to the nerves of the zygomatic plexus, and several venous 

 and arterial vessels ; by its deep face, to the inferior maxillary bone, the 

 alveolo-labialis and maxillo-labialis muscles, the superior molar glands, and 

 largo venous branches ; by its inferior border, with the parotid canal, 

 and the glosso-facial artery and vein ; by its superior and posterior border, 

 to the parotid gland. Its deep plane responds, anteriorly, with the temporo- 

 maxillary articulation, and is so intimately confounded with the temporalis, 

 that it is impossible to define the respective limits of the two muscles. 



n. This muscle, the special elevator of the lower jaw, plays an 

 important part in mastication. It always acts as a lever of the third class, 

 the middle line, which represents the resultant of all its constituent fibres, 

 passing behind the last molar. 



2. Temporal or Crotaphitic Muacl- . 

 Synonyms. Temporo-maxillnris ftt'rord. (The temporo-maxillarii of Leyh.) 



>t inn -Form Structure. Situated in the temporal fossa, to which 

 it is moulded, and which it fills, this muscle is flattened from above to 

 below, divided by strong tendinous intersections, and covered by a nacrous 

 aponeurotic layer. 



x. - It tak.-s its origin: 1. In the t. nq> iv.l fan :i'i>l . n flu 



