28 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Function: Rotator of the head. 



The trapezius will be treated with the muscles of the upper extremity 

 for functional and topographical reasons. 



Comparative anatomy of the vago-accessory group. — The find- 

 ings of Lampert (1926) in the three pharyngeal constrictors of a male 

 Mycetes auratus ( =Alouatta seniculus) and a female Mycetes helzehuth 

 ( =Alouatta belzebul) are like those I described. Sandifort (1834) noted 

 the strong development of the constrictor musculature of the pharynx, 

 particularly the part attached to the thyroid cartilage. The three 

 constrictors in Ateles, Cebus, and Lagothrix (Lampert, 1926) are com- 

 parable to those of the howler but smaller, in harmony with the lack 

 of enlargement of the larynx and the hyoid. Both Cebus and Ateles 

 have an m. intercornualis (Lampert, 1926). 



Extraocular Group 



There are only seven muscles concerned with the motility of the 

 eyeball in Alouatta, namely, a m. levator palpebrae superioris, two 

 obliqui and four recti (fig. 10). In agreement with Ottley (1879), who 

 says that a m. retractor bulbi is absent in platyrrhines, I did not 

 find it in the howler. Sirena (1871) states that these muscles agree 

 with those of man. 



M. levator palpebrae superioris: This muscle arises from the upper 

 margin of the optic foramen above the attachment of the common 

 tendon and lateral to the origin of the superior oblique. Its fleshy 

 fibers pass forward as an initially small stalk, but soon fan out into a 

 thin muscular layer which enters the upper lid and ends within its 

 substance. The muscle lies between the periorbita and the rectus su- 

 perior. A branch of the oculomotor nerve penetrates its deep surface 

 to supply it. 



M. obliquus superior: Origin is by fleshy fibers from the upper 

 root of the alisphenoid, medial to the previous muscle and above the 

 common tendon. It forms a round, long belly which runs forward 

 along the medial orbital wall above the rectus medialis. This reaches 

 the pulley where the muscle thins down into a round tendon which 

 turns laterally between the rectus superior and the eyeball. Insertion 

 takes place behind the equator in the posterolateral quadrant. N. 

 trochlearis enters the lateral surface of the superior oblique near the 

 origin of the muscle. 



M. rectus superior: It arises by the anulus tendineus communis 

 through which its fibers are attached to the upper margin of the optic 

 foramen below the origin of m. levator palpebrae superioris. It runs 

 forward and is inserted as a thin membrane into the sclera, about one- 

 quarter or one-third of the way between the equator and the corneo- 

 scleral junction. The main axis of this muscle forms an acute angle 



