100 THE STRUCTURE OF MAX 



an anterior tract. The former arises from the pelvis, and is 

 inserted anteriorly, as a rule, on a level with the fifth rib ; the 

 latter is represented by the ventral cervical muscles, viz. the 

 sterno-hyoid and sterno- thyroid, which here and there bear 

 inscriptiones tendineae indicative of their former segmentation. 

 To these must be added the almost constant omo-hyoid, which 

 is provided with an inscriptio, and the thyro-hyoid. Farther 

 forward these are joined by the hyo-glossus, genio-hyoid and 

 genio-glossus, which belong to the same metameric series. 1 



In the lower Primates the rectus abdominis muscle still 

 reaches to near the first rib, and thus recalls the connection 

 with the cervical musculature mentioned above, which was first 

 lost in the Reptiles. Even in Man it may sometimes run beyond 

 the fifth rib and, under cover of the pectoralis major, pass as far 

 up as the second. This is a striking case of atavism. 



In the higher Primates the thoracic head of this muscle 

 shifts back to the lower ribs, and this shifting towards the 

 abdominal region is accompanied by an advancing loss of 

 segmentation in both the Anthropoids and Man. 2 But even 

 where this is most marked the muscle has not quite lost its 

 thoracic character. 



This retreat of the rectus muscle is intimately connected 

 with the development of the great adductor of the fore-limb (the 

 pectoralis major), since it is only when the upper parts of the 

 rectus disappear that the muscular bundle forming the pectoralis 

 major and, indeed, that forming the pectoralis minor as well 

 is able to take possession of the firm anterior thoracic surface 

 furnished by the ribs. Where, as in the lower Apes, the anterior 

 end of the rectus muscle covers the thorax as far as the lateral 

 edges of the sternum, a primitive condition being thus retained, 

 those fasciculi of the pectoral muscles which arise from the 

 skeleton come simply from the sternum. " We here have a con- 

 flict at close quarters between different parts of the organism " 

 (Huge). 3 



In connection with his studies of the abdominal musculature, 



1 [Cf. Albrecht. Beitrag z. Morphologic des M. omo-hyoides u. d. ventr. inneren 

 Interbranchialmusculatur i. d. Reihe d. IVirbelthiere. Inaug. Diss., Kiel., 1876.] 



2 In many cases the muscle withdraws in a distal direction even farther than 

 the fifth rib, and derives its anterior (uppermost) slip from the sixth. A primitive 

 slip from th eighth rib may also be retained (Ruge). 



3 Where, as a rare anomaly, the rectus abdominis is double on one or on both 

 sides, a very low condition is indicated, this arrangement being typical in Amphibia 

 and Saurians. 



