MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 



171 



has extended its insertion beyond the acromion on to the clavicle 

 in Ateles (Ashton and Oxnard, 1963, Campbell, 1937; Hill 1962), 

 Brachyteles (Hill, 1962), Lagothrix (Ashton and Oxnard, 1963; 

 Campbell, 1937; Hill, 1962; Robertson, 1944), and Alouatta, but 

 only in the howler is its cranial origin extensive (table 1). It extends 

 from the occipital protuberance to the middle of the nuchal crest 

 (fig. 5). This character I regard as an adaptation of the trapezius 

 to act as an extensor of the neck. The greater thickness of the cranial 

 portion of the muscle is another detail in common with the Atelinae. 



Table 1. — Data for Ccbus {climber or quadruped), Lagothrix, Brachyteles, and 

 Ateles {hrachiators or semibrachiators) and Alouatta* (Pluses = degree of 

 development: + + + ='larger, + + ^intermediate, += lesser, ?=unknown.) 



•Summarized from Ashton and Oxnard, 1963; Campbell, 1937; Hill, 1960. 1962; Robertson, 1944; Schuck, 

 1913a; Sirena, 1871; this work. 



275-199 O - 68 - 12 



