MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 



47 



Sirena (1871) says that this muscle is just as in man, but I could not 

 verify a C 3 origin which is usually assigned to it. 



Nerve supply: Branches from the ventral rami of C IV to VI. 



M. scalenus medius (figs. 16, 17): It is the largest of the three 

 scalenes and separated from the anterior by the brachial plexus and 

 the subclavian artery. Its origin is by fleshy digitations from the 

 anterior tubercle of C 1 to C 6. The muscle broadens in approaching 

 the dorsolateral aspect of the thorax and is anteroposteriorly flattened 

 throughout. It passes superficial to the first two costal digitations of 

 the serratus anterior but under cover of the others (fig. 17). A slip 

 separates off the belly in the neck to be inserted on the anterior 

 tubercle of C 3. The thoracic ending involves a variable number of 

 ribs to which digitations are sent from the deep surface of the muscle. 

 Insertion is on the second, third, and fourth ribs in two males and the 



MAS. 



Figure 16. — Scalene muscles (1, reinforcing bundle to m. scalenus medius; 2, m. scalenus 

 brevis posterior; 3, m. scalenus medius; 4, m. levator costae primus; 5, m. scalenus medius 

 accesorius; 6, m. scalenus brevis anterior; 7, m. atlantoscapularis anterior.) 



