PHYSIOLOGY, AM> PATHOLOGY OF THE CHIMPA^ZEE. 341 



thoracic and lower cervical regions they are filled ; and the com- 

 bined mass eventually breaks vip again into muscular slips. 

 The inner column separates off in the upper thoracic region. 

 The ilio-costalis (text-fig. 33, I-C.O) arises with the subjacent 

 longissimus from the iliac crest between the highest point and 

 the posterior superior spine, and it derives fibres from the 

 covering posterior lamella of the lumbo-dorsal fascia. It gives 

 two slips to the lower boiders of the twelfth and thirteenth ribs, 

 of which the former is the larger. It receives a large number of 

 muscular slips from the outer surfaces of all the ribs, the size 

 of the latter diminishing from below upwards. Many of the small 

 muscular slips are continuous with the slips given oflf from the 

 longissimus. From the outer border of the muscle long, slender 

 tendons run to the lower borders of the angles of the first nine 

 ribs. The longissimus (text-fig. 33, Lo.C) arises from the crest 

 of the ilium from the highest point to the posterior superior 

 spine, the posterior sacro-iliac ligament, the back of the sacrum, 

 all sacral and lumbar vertebral spines and the spines of the 

 twelfth and thirteenth dorsal vertebrae. It gives slips to the 

 lower borders of ribs 4 to 13 between their angles and the 

 transverse processes. The attachments to the first three ribs come 

 from the combined longissimus and ilio-costalis. The combined 

 outer and middle columns divide into slips which are attached to 

 the posterior tubercles of the transverse processes of the third, 

 fourth, and fifth cervical vertebrae along with the levatoi- angulse 

 scapulae. The third cervical vertebra thus receives splenius 

 cervicis, levator anguli scapulae and longissimus. The part of 

 longissimus attached to these processes corresponds to longissimus 

 cervicis in Man, but is not so extensive. The spinalis dorsi 

 (text-fig. 33, S.C) is a narrow muscle arising from the longissimus 

 dorsi and the eleventh and twelfth dorsal spines. It is inserted 

 by muscular and tendinous fibres into the first eight dorsal spines. 

 Between it and the longissimus is a triangular space into which 

 the complexus passes and fuses with both. The longissiimts capitis 

 (text-fig. 33, L.Cap) is relatively stronger than in Man. It arises 

 from the first six dorsal transverse processes by tendinous and 

 muscidar slips. It is fused with the longissimus dorsi, complexus 

 and scalenus posticus. It breaks up into slips which are inserted 

 into the po.sterior tubercle of the atlas and the occipital bone 

 below the crest. On the atlas its insertion is fused with the 

 levator scapulae and omo-trachelian. 



The complexus (text-fig. 34 A), lying under the longissimus 

 capitis, has a very extensive origin from the articular processes of 

 the lower five cervical vertebrae, the upper six dorsal transverse 

 processes and the longissimus and spinalis dorsi. It forms 

 a number of closely-set paiuUel muscle bundles which are in- 

 serted into the inner half of the occipital bone below the superior 

 curved line. It is not separable into a biventer cervicis and 

 complexus as in Man. No slip springs from the seventh cervical 

 spine. 



Proc. Zool. Soc— 1923, No. XXIII. 23 



