32 U.S. NATIONAL MUSEUM BULLETIN 2 73 



rupted condition between the two muscles of his adult female spider. 

 The muscle is also weakly differentiated in Brachyteles (Hill, 1962). 

 The styloglossus is present in Cebus (Lampert, 1926), Ateles (Bijvoet, 

 1908; Houpert, 1927; Lampert, 1926), Lagothrix (Lampert, 1926) 

 and Brachyteles (Hill, 1962). The variabiUty of this structure in 

 Alouatta indicates, perhaps, that it has not yet attained a stable 

 pattern in this genus. 



Muscles of the Trunk 



Expaxial Musculature 



The epaxial group of muscles supplied by the dorsal rami of the 

 spinal nerves occupies the regions between the back of the skull and 

 the end of the tail. They are contained in the neck and trunk Avithin 

 the space formed by the nuchal and thoracolumbar fasciae with the 

 vertebrae and part of the ribs. A tough fibrous fascial continuation 

 of the first two into the tail surrounds the caudal muscles, forming 

 sheaths for their many tendons. 



The nuchal and thoracolumbar fasciae (figs. 11, 12): An extensive 

 aponeurotic lamina covers the splenius and the erector spinae. It is 

 particularly strong and evident in the low thoracic and lumbar regions. 

 Its fibers arise from (1) the ligamentum nuchae, (2) spines of the lower 

 cervical, all thoracic and lumbar vertebrae, (3) the corresponding inter- 

 spinal ligaments, and (4) the crista sacralis mediana. These fascicles 

 follow a laterally transverse direction to end (1) on the whole extent of 

 the nuchal crest under cover of the origins of trapezius and rhom- 

 boideus, (2) in the cervical region, on the posterior tubercle of all 

 transverse processes, (3) in the thorax, on the body of each rib just 

 lateral to the attachment of m. iliocostalis, and finally, (4) in the loins, 

 the fibers of the fascia turn medially at the lateral border of the 

 erector mass and lining its deep surface reach the tip of all lumbar 

 costal processes. Both the latissimus dorsi and the posterior inferior 

 serratus arise from the thoracolumbar part which also gives rise to 

 the bundles of the internal oblique and transversus abdominis (figs. 11, 

 12). The lateral attachment of the sacral fascicles of the fascia is on 

 the Uiac crest, from the posterosuperior iliac spine dorsaUy to the 

 craniad projecting spine of the crest ventrally. This last structure is 

 described with the insertions of m. obliquus externus abdominis. 

 Between the median sacral crest and the iliac tuberosity the fascia is 

 thin and fused with the underlying tendinous superficial fibers of the 

 erector spinae and the caudal musculature. In the neck m. splenius is 

 contained within a split of the nuchal fascia which in both the cervical 

 and thoracic regions sends a sagittal septum between the iliocostalis 

 and longissimus muscles. 



