52 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Mm. intercostale interni: Their fibers run at right angles to those of 

 the externals. Ventrally, they reach the sternum in the upper six 

 spaces and lower down, the costal cartilages of the seventh to the 

 last rib as these form the caudal margin of the thoracic cage. Dorsally, 

 the internals end at some distance from the costal tubercle, the rest 

 of the intercostal space being filled by the thin membrana intercostalis 

 interna. 



M. transversus thoracis: It lies on the deep aspect of the ventral 

 thoracic A\all and arises at each side of the midline from the lateral 

 border of the four lower sternal pieces, excluding the xiphoid process. 

 The same number of flat and thin muscular slips is formed, running 

 laterally. The lower of these digitations crosses the seventh and sixth 

 cartilages and takes additional origin on the last before ending on the 

 fifth. The second and third digitations have a similar arrangement 

 with attachments to the fourth and third cartilages, respectively. The 

 fibers of the first have a rather steep craniolateral orientation and are 

 inserted by thin tendinous fascicles on the second costal cartUage. 



Mm. subcostales: Only three such muscles are present at eacli 

 side in the upper part of the thorax. Typically, a subcostal arises on 

 the pleural surface of the body of one rib and its fibers pass caudo- 

 medially to be inserted on the body of a rib two costal segments 

 removed. The first connects ribs 1 and 3, the second 2 and 4, and the 

 third 3 and 5. 



The pattern of all these muscles in Mycetes juscus {—Alouatta fusca) 

 as described by Sirena (1871) is similar to my findings in the seniculus 

 species. 



Nerve supply: All these thoracic muscles receive branches from 

 the corresponding intercostal nerves. 



Function: By their known action upon the ribs all these muscles 

 are accepted as active in the respiratory movements. 



M. ohliquiis externus abdominis (fig. 17) : The more superficial of 

 the broad abdominal muscles is a wide and long, partly muscular, and 

 partly aponeurotic sheet extended from the rib cage to the os coxae in 

 a craniocaudal direction and from the thoracolumbar fascia to the 

 linea alba transversely. It arises by a variable number of fleshy digita- 

 tions from the external surface of ribs 5-13 in a 14-rib male, 4-14 in 

 a 14-rib male, 4-13 in a 13-rib male, and 4-13 in a 13-rib female. This 

 origin follows a concave line open craniodorsally. It begins at about 

 the middle of the fourth or fifth costal body and ends on the tip of the 

 last rib cartilage involved in the origin. The fascicles interdigitate 

 with those of m. serratus anterior (ribs 4-8) and m. latissimus dorsi 

 (ribs 9-12). Some isolated fibers may reach the thoracolumbar fascia 

 between the last rib and the coxal bone. The upper bundles of the 

 muscle have a slight caudoventral slant, the lower ones descend almost 



