MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 35 



beyond a plane passing through the tip of the costal processes in the 

 loins and just short of the costotransverse articulations in the thorax. 

 In the former region a sagittal septum given off from its deep aspect is 

 inserted on a poorly marked line which joins the anapophysis and 

 metapophysis in each vertebra (fig. 11). This partition I call the 

 attached sheet of the aponeurosis which is thereby divided into a 

 medial and a lateral half. Kohlbrugge (1897) describes a similar struc- 

 ture in Semnopithecus (= Presbytis) and the pongids, emphazising the 

 distinctness of this aponeurotic lamina from the fascia lumbodorsalis 

 (thoracolumbar fascia). Howell and Straus (1933) did not establish 

 this difference between the thoracolumbar fascia and the aponeurosis 

 sacrospinalis in the rhesus monkey. According to them, both m. 

 longissimus and m. spinalis arise from the deep surface of the lum- 

 bodorsal aponeurosis. 



M. iliocostalis (figs. 11, 12, 13): The more lateral part of the long 

 system has two portions: (1) M. iliocostalis lumbothoracis. Origin 

 is by fleshy fibers from (a) the iliac crest and the cranially projecting 

 spine, and (b) the lateral surface of the attached sheet and under 

 surface of the sacrospinal aponeurosis on its lateral half (fig. 11). 

 Additional fibers are contributed to the deep siu"face of the muscle 

 in the form of fleshy digitations arising from most if not all ribs. 

 The lumbar insertion is by fleshy bands attached to the costal processes 

 and the last two or three ribs. In the thorax, m. ilicostalis forms 

 several tendons at its lateral border and these end on a small spine 

 found at the angle of approximately the first nine ribs. The distance 

 between the angle and the tubercle is increasingly reduced toward 

 the neck until these two points are very close in the first rib. The 

 highest tendon reaches the posterior tubercle of C 7. (2) M. iliocostalis 

 cervicis lies medially to the cranial part of the lumbothoracis and 

 arises by fleshy slips from the first three ribs. The short fusiform beUy 

 inserts by two tendons on the posterior tubercle of the fifth and sixth 

 cervical vertebrae. 



M. longissimus (figs. 1 1, 12, 13, 14) : It lies medial to the iliocostalis 

 from which it is separated in the thorax and neck by the sagittal sep- 

 tum of the nuchal and thoracolumbar fasciae, and in the loin by the 

 attached sheet of the sacrospinal aponeurosis. The muscle is composed 

 of two parts: (1) M. longissimus lumbothoracis arises in the lumbar 

 region from the sacrospinal aponeurosis both on the under surface of 

 its medial half and medial aspect of the attached septum. In the thorax 

 its superficial fleshy fibers are a continuation of the aponeurosis sacro- 

 spinalis. The muscle receives additional contributions from the meta- 

 pophyses of the first two lumbar and last two or three thoracic verte- 

 brae. Up in the high thoracic region it occasionally has muscular 

 fascicles coming from the metapophyseal tubercles of T 1 to T 3. The 



