MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 37 



long mass formed from these different sources reaches the neck as a 

 cervical extension and gives off digitations from its deep surface to the 

 underlying bony structures. Mediocranially oriented fibers separate 

 toward the anapophyses of all lumbar and thoracic vertebrae (only 

 anapophyseal tubercles are involved in the first thoracic segments). 

 The cervical extension sends sUps of the same direction to the posterior 

 tubercle of all cervical vertebrae, although C 1 is usually excluded. 

 These insertions are entirely fleshy on the lumbar and lower thoracic 

 regions, increasingly tendinous in the thorax and again muscular in the 

 neck. Fibers with laterocranial direction leave the deep surface of the 

 muscle and run toward the lower border of all ribs where they are in- 

 serted between the tubercle and the midpoint between the tubercle 

 and the angle. These digitations are flat and broad, fleshy caudally up 

 to about the ninth rib, but increasingly tendinous in the thorax. The 

 last one or two ribs may not receive any. (2) M. longissimus cervicis et 

 capitis. These two commonly distinct muscles are more or less fused 

 into a single mass in Alouatta. It lies medial to the cervical extension of 

 the lumbothoracal part and arises by fleshy fibers from (a) the crest 

 formed by the articular processes of the last five or six cervical verte- 

 brae, and (b) the first three or four metapophyseal tubercles where 

 they are partially fused with the attachments of the cervical extension. 

 Insertion takes place after a craniolateral path into the posterior 

 tubercles of the last six cervical vertebrae and by a large round tendon 

 on the postmastoid crest (fig. 5) . 



M. spinalis (figs. 11, 12) : It is the more medial component of the 

 long system lying between m. longissimus and the spines of all cervical, 

 thoracic, and lumbar vertebrae. It is divided into two parts. (1) M. 

 spinalis lumbocervicalis is covered by the sacrospinal aponeurosis and 

 itself lies over the deep oblique musculature. The long mass has a 

 segmented arrangement and extends from about S 2 up to the neck. 

 In the sacral and lumbar regions fleshy fibers arise from the under 

 surface of the sacrospinal aponeurosis medially to the origins of 

 longissimus and are inserted on the spinous processes. Those close to 

 the midline are quite short, whereas the more lateral fascicles extend 

 for a longer distance and form a deep tendon which ends on a spine 

 about five vertebrae cranial to its origin. This attachment lies in close 

 relation to that of the corresponding segment of the deep oblique 

 system. In the upper thoracic and cervical regions the fibers of m. 

 spinalis arise from the sacrospinal aponeurosis and those closer to the 

 midline from the corresponding vertebral spines. The segments are now 

 shorter, bridging only three vertebrae, and do not have tendinous 

 endings. Highest insertion is on the spine of C 4 or 5. (2) M. spinalis 

 capitis is formed by fascicles arising from the aponeurosis and the 

 spinous processes of C 6 to T 4. They constitute a volumiuous muscle 



