The Muscular System 



of the 

 Red Howling Monkey 



Introduction 



The howling monkeys, which are members of the superfamily 

 Ceboidea (Simpson, 1945), inhabit a very extensive area in the 

 tropical and subtropical forests of Central and South America. They 

 are well known among travelers and naturaUsts for their prodigious 

 roars, which can be heard for very long distances. The voice-producing 

 organs have been extensively studied in the past. The pertinent 

 bibUography can be found in the sunmiary account of Starck and 

 Schneider (1960) and the recent study by Kelemen and Sade (1960). 

 Schon (1964a) added further information about the pharyngolingual 

 musculature of this animal and emphasized certain functional aspects 

 of these structures. The muscular system of the whole animal was 

 investigated by Santi Sirena (1871), who compared it with man, 

 the great apes, and some catarrhine monkeys; unfortunately, this 

 work has remained little known among modern students of primate 

 anatomy. Sirena used three specimens preserved in alcohol. They 

 were tentatively classified as Mycetes fuscus, a synonym for the 

 accepted name Alouatta fnsca (Hershkovitz, 1964). Two were males, 

 but Sirena could not ascertain the sex of the other animal because 

 its genito-urinary organs had been removed. Each one had fourteen 

 pairs of ribs, and at least one was an adult. 



The purpose of my research was to compare the entire muscular 

 system of Alouatta with that of the spider, woolly, and woolly spider 

 monkeys, on the one hand, and the capuchin on the other. All of these 

 animals have prehensile tails. The howler is usually grouped with 

 Ateles, Lagothrix, and Brachy teles as a brachiator (Erikson, 1963) or 

 as a semibrachiator (Ashton and Oxnard, 1963). Cehus is classified 

 as a chmber (Erikson, 1963) or as a quadruped (Ashton and Oxnard, 

 1963). It is hoped that by contrasting the differences and similarities 

 between the howUng monkey and the other four, the muscular adap- 



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