18 U.S. NATIONAL MUSEUM BULLETIN 2 73 



and the caninus part of the caninus-triangularis complex.. The fascicles 

 radiate out toward the mouth and nose, the anterior ones (pars labialis) 

 reaching the upper lip where they end by intermixing mth the orbicu- 

 laris oris, the more posterior (pars nasalis) on the fascia deep to the 

 nasolabiahs around the apertura piriformis and the dorsum of the 

 nose. In one male the pars nasalis and pars labialis on both sides of 

 the face were individually discrete bands separated by a hiatus. 

 The muscle is a common feature among known platyrrhines (Schreiber, 

 1928). 



M. orbicularis oris: It is formed by abundant muscular bundles 

 of variable length which pass from the labial skin to the mucosa and 

 vice versa, surrounding the oral aperture (fig. 1). A rather broad 

 lamina is thus formed within the lips, thinner in the upper where it 

 occupies the space between the free border and the piriform opening, 

 thicker in the lower and filling the whole l^p. 



M. caninus: This is a triangular and strong sheet extended from 

 the paranasal to the oral region across the infraorbital (fig. 1). It 

 lies deep to the maxillonasolabialis and to the infraorbital vessels 

 and nerve. Origin is from along the naso- and premaxiUomaxillary 

 sutures. Its fibers run do^vn and laterally toward the upper lip and the 

 angle of the mouth ; the more anterior follow the same direction as those 

 of the orbicular with which they seem to form a single muscular layer. 



M. triangularis: It has a variable development (fig. 6). In two 

 males it is formed by many fibers which are continuations of the 

 caninus. They become superficial near the angulus oris by passing 

 stepmse through those of the zygomatico-orbitalis-platysma complex. 

 Their ending is on the skin of the region \vdth the anterior fibers 

 following the direction of the orbicularis and the posterior ones diverg- 

 ing at an angle from the corner of the mouth. In the other male the 

 triangularis was not present as a superficial structure and in the female 

 the muscle was rather weak. Ruge (1887) says it is absent in Mycetes 

 (=Alouatta sp.). 



M. buccinator: In agreement with Schreiber (1928) and contrari- 

 wise to Ruge (1887), I found this structure a complicated arrangement. 

 The well developed muscle lies in the buccal region covered by m. 

 platysma and the zygomaticoorbital plare. It is organized in three 

 layers each with different fiber direction (fig. 1) : (1) Superficial bundles 

 are present only in the oral half of buccinator where they form a 

 laterally compressed belly of variable development and even in the 

 same individual its magnitude may be different bilaterally. Typically, 

 these fascicles run from the alveolar border of the maxilla to that of 

 the mandible following a vertical and rostraUy concave path. They 

 are separated from the orbicularis oris by the platysma-zygomatico- 

 orbital complex and appear to be a part of the first muscle after re- 



