316 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



Innervation. — A branch from an anastomosis of R. maxillaris inf. 

 trlgemini and R. hyoideo-mandibularis facialis. 



Action. — Prevents the separation of the rami of the mandibles 

 whether from pressure within or from the action of the lev. arcds 

 palatini. 



II.— MUSCLES OF THE PALATINE ARCH. 



1. Levator A kcus Palatini, (No. 24, Cuv.; Lev. suspensorii, Stan.; 



Lev. tympani, Ow.) (Figs. 1 & 2, LAP). 



This is exposed on cutting through the upper and posterior 

 portions of the insertion of the add. mand., and reflecting it. 

 The muscle may be described as consisting of two parts. The 

 anterior portion is triangular and thick, and arises from the poste- 

 rior border of the antorbital process and from the inferior surface 

 and the edge of the ectethmoid and frontal. Its fibres arching 

 over the orbit and passing below the add. mand., unite to a tendon, 

 which is inserted into the extremity of the transverse ridge of the 

 hyomandibular. The posterior part is quadrangular and thin, and 

 arises from the edge of the sphenotic. Those fibres arising from the 

 rudimentary postorbital process are at first tendinoiis but soon be- 

 come muscular, and, along with the more anterior ones, pass directly 

 downwards to be inserted along the whole upper surface of the trans- 

 verse ridge on the hyomandibular, a few fibres passing to the surface 

 of the bone above the ridge. 



Innervation. — It is supplied by a branch from an independent 

 strand of the trigeminus which accompanies the R. maxillaris sup. 



Action. — It raises the palatine arch. The anterior triangular por- 

 tion will also pull it forwards. 



This muscle is very similar in its relations to that of Esox, but dif- 

 fers slightly from that of other forms. The innervation differs also 

 slightly, Vetter describing it in the forms he studied as being by a 

 branch from the R. maxillaris inferior. Here, however, the inde- 

 pendent strand must be equivalent to this branch, since like it it 

 also supplies the dilatator operculi. The great differentiation which 

 the trigeminus shows accounts for these slight dissimilarities. 



2. Adductor Arcus Palatini, (No. 22, Cuv. ; Constrictor, Stan. ; 



Depressor tympani, Ow.) 

 This consists of two distinct parrs. The posterior portion is ex- 

 posed by removing the branchial and lower part of the hyoid appara- 



