30 U.S. NATIONAL MUSEUM BULLETIN 2 73 



M. rectus medialis: Arising from the medial border of the optic 

 foramen by means of the tendinous ring, its large transversely flat- 

 tened belly runs forward below that of m. obliquus superior. The 

 ethmoidal branches of the nasociliary nerve accompanied by the 

 corresponding vessels separate the two muscles. Insertion is by an 

 aponeurotic expansion on the medial side of the sclera rostrally to 

 the equator. The lower division of the oculomotor sends a branch to 

 the lateral aspect of the muscle. 



M. rectus inferior: It lies on the floor of the orbit between the 

 periorbita and the eyeball with its fascial sheath. Origin is by the 

 tendinous fibers of the common ring from the lower border of the 

 optic foramen. The long belly passes forward to be inserted on the 

 sclera in front of the equator and in line with the attachment of m. 

 rectus superior. The lower division of the oculomotor nerve innervates 

 this muscle. 



M. obliquus inferior: It has a fibrous origin at the lower part of 

 the posterior lacrimal crest from which a narrow and tendinous band 

 is directed medially and gives rise to the fleshy bundles of the muscle. 

 Its expanded belly crosses the insertion of the rectus to end on the 

 sclera. It is supplied by the lower division of the oculomotor nerve. 



Lingual Group 



There is a torus on the inner surface of the howler's mandible. It 

 is continuous with the linea mylohyoidea and forms the upper margin 

 of a variably developed simian pit (see Scott, 1963). This is sub- 

 divided by a short sagittal crest running from the torus to the basis 

 mandibulae which constitutes the lower margin of the depression. 



M. genioglossus: This paired muscle arises at each side of the midline 

 from the corresponding subdivision of the simian pit (fig. 5). It is 

 initially formed by mixed fleshy and tendinous fibers arranged into 

 a craniocaudally compressed structure. The muscular fascicles are 

 directed toward the tip, lower surface and root of the tongue (fig. 7). 

 Fibers along the midline intercross with those of the intrinsic lingual 

 muscles and are inserted on the lateral aspect of the medial lingual 

 septum. The lateral bundles of the genioglossus reach the hyoglossal 

 membrane after forming an elongated belly under cover of m. hyo- 

 glossus, below the intrinsic lingual musculature and above the genio- 

 hyoid and the hyoid bulla. Sirena (1871) describes two portions in 

 this muscle, the genioglossus proper and that which he calls genio- 

 hyoideus profundus. The first goes from an origin equal to the one 

 I found, to the tongue and hyoglossal membrane, the deep part 

 attaches to the hyoid bulla. 



Nerve supply: N. hypoglossus. 



Function: Its contraction pulls the root of the tongue and the 



