50 U.S. NATIONAL MUSEUM BULLETIN 2 73 



muscle he describes as mm. intertransversarii longi in Ateles corre- 

 sponds, in my opinion, to the scalenus brevis posterior of Alouatta. 

 He claims that such a structure is part of the iliocostalis, which in 

 his spider monkey reaches only rib 1 cranially. According to Hill 

 (1962) all three scalenes are present in Brachy teles. Their arrangement 

 is comparable to that of the howler and the costal attachment of the 

 scalenus medius is on ribs 2 to 5. 



It is interesting to note that the scalenus medius has approximately 

 the same extension over the thorax in all these platyrrhines. Of the 

 four genera for which information is available in this respect, one, 

 Ateles, is a very specialized brachiator, and another, Gebus, a fairly 

 generalized arboreal quadruped. 



Mm. serrati posteriores: The serratus posterior inferior lies over 

 the caudal half of the thorax just lateral to the sacrospinalis and 

 almost entirely covered by m. latissimus dorsi (fig. 17). Its fleshy 

 fibers arise from the thoracolumbar fascia by means of a short apo- 

 neurotic sheet which is partially fused to the overlying one of the 

 latissimus (fig. 12). The muscular fascicles run almost transversely 

 laterad forming a variable number of digitations which are inserted 

 on the distal border of the ribs just beyond the angle. Seven such 

 slips attach to ribs 8 to 14 in two 14-rib males; only sLx are found 

 in the 13-rib male, inserted on ribs 8 to 13. The 13-rib female had 

 eight attached to ribs 6-13. The caudal two or three endings inter- 

 digitate with the origins of m. obliquus abdominis externus and are 

 covered by the latissimus dorsi. The serratus posterior superior is 

 represented by transversely directed tendinous fibers more or less 

 fused to the thoracolumbar fascia and running from ribs 2-5 toward 

 the dorsal midline. 



Sirena (1871) also found the serratus posterior superior replaced 

 by aponeurotic fibers. They extended across the erector spinae between 

 the spines of C 5 to T 2 and ribs 1 to 4. On the other hand, Ogushi 

 (1920) claims to have seen in one Mycetes seniculus (=Alouatta 

 seniculus) fleshy fibers attaching to ribs 3 to 4 with aponeurotic 

 fascicles inserted on ribs 2 and 5. The serratus posterior inferior of 

 Mycetes fuscus {— Alouatta fn sea) is said by Sirena (1871) to be even 

 better developed than in man, extending from the spines of the 

 loA\'er six thoracic and first two or three lumbar vertebrae to the 

 last nine ribs, except the fourteenth. According to Ogushi (1920), 

 the costal insertion of the inferior serratus is by fleshy fibers on ribs 

 8 to 12 and tendinous on tlie seventh and thirteenth in a 14-rib 

 Mycetes seniculus {=Alouatta seniculus). Neither of these two authors 

 indicates an attachment to the last rib. It should be repeated that 

 this digitation Axas found ah\"ays in both sides of the four animals 

 I studied. It can, nevertheless, be missed because it is almost entirely 

 covered by the slip to the next rib craniad. 



