MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 41 



three specimens of Mycetes juscus (=Alouatta fusca) studied by 

 Sirena (1871) had an iliocostalis cervicis. The sacrohimbalis reached 

 only the transverse processes of C 7. 



According to Sirena (1871), a m. longissimus dorsi (m. longissimiis 

 lumbothoracis) has an origin from the dorsal surface of the sacrum 

 and one insertion, by means of aponeurotic fibers, on the spinous 

 processes of the last nine thoracic vertebrae. The description agrees 

 in other details with mine. The sacral origin I regard as doubtful, and 

 probably is an error. The lateral sacral canal is occupied by m. extensor 

 caudae lateralis which is clearly separated from the longissimus, and 

 the medial canal is taken by the extensor caudae medialis. The 

 aponeurotic ending on the thoracic vertebrae is more likely a misin- 

 terpretation of the sacrospinalis aponeurosis in that region. Sirena 

 (1871) describes a m. transversaUs cervicis (m. longissimus cervicis) 

 and m. complexus minor (m. longissimus capitis) separately but adds 

 that these two muscles are fused. The origin of the first is assigned 

 to the transverse processes of the first two or three thoracic vertebrae 

 and C 7. Sirena (1871) does not cover m. spinalis at aU. In the tail of 

 Alouatta jusca a m. sacrococcygeus superior corresponds to the 

 extensor caudae lateralis and an m. ileococcygeus superior to the two 

 abductors. 



Nerve supply of the long system. — The muscles of the long 

 system are aU supplied by the dorsal rami of the corresponding spinal 

 nerves; in the cervical and upper thoracic regions by the lateral 

 branches of these rami, in the lower thoracic and lumbar by their 

 medial branches, and in the taU by the dorsal branches of the corre- 

 sponding sacral and caudal nerves. 



Deep Oblique System 



The muscles of this group are not well differentiated except for 

 m. semispinalis capitis, the rotatores, and the extensor caudae 

 medialis. The total mass appears to be small in relation to that of 

 the long system, and all its fibers are craniomedially directed from 

 metapophyses to spinal processes. 



M. semispinalis lumhocervicalis et multifidus: This is a compact and 

 segmentally arranged column present along the vertebral grooves of 

 the upper lumbar, thoracic, and cervical regions. Its caudal limit has 

 been arbitrarily assigned to the metapophysis of either L3 or 4, as the 

 whole transversospinal system is continuous with the medial caudal 

 extensor without apparent interruption. The fibers of one segment 

 arise from a metapophysis and proceed cranially to insert on the tip 

 and caudal border of a spinous process five (thoracocervical portion) 

 or sLx (lumbothoracal portion) segments removed from their origin. 

 The deeper fibers of each unit bridge only three or four vertebrae and 



