310 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



costal cartilages, beneath the axillary border of the peetoralis 

 major. This is its normal condition in most mammals, but in 

 man it is commonly fused with, and forms part of, the peetoralis 

 major. 



(5) The sternalis is a new muscle. The peetoralis major is 

 formed from the same ventral longitudinal sheet as the rectus 

 abdominis and sterno-mastoid. The fibres of the sternalis, which 

 lie along the sides of the sternum, superficial to the origin of the 

 peetoralis major, represent a persistent part of the primitive 

 longitudinal sheet. The sternalis is a derivative of the sphincter 

 colli, part platysma-sheet (Parsons). 



(6) In the sterno-mastoid, four elements are recognised : sterno- 

 mastoid, sterno-occipital, cleido-mastoid, cleido-occipital. The 

 cleido-occipital fibres, which form part of the same sheet as the 

 trapezius, are often absent. On the other hand the cleido- 

 occipital fibres may be continuous with the trapezius. 



(7) The peetoralis minor is sometimes inserted to the capsule 

 of the shoulder and great tuberosity of the humerus. This is 

 the primitive insertion of the muscle. The coracoid insertion is 

 a secondary attachment seen only in man and some of the higher 

 primates. "When the peetoralis minor is inserted to the 

 coracoid, the former fibres of insertion become fused with, and 

 forms part of, the coraco-humeral ligament. The coraco-humeral 

 ligament represents the ischio-capsular of the hip joint. 



(8) In some apes (such as the Gibbons) the biceps has four 

 heads — the two usual, the long and short, and two others, one 

 from the inner border of the humerus and one from the bicipi- 

 tal groove. These two extra heads appear frequently in man. 



(9) The epitrochieo-anconeus is frequently present. It crosses 

 the ulnar nerve from the internal condyle to the olecranon. 



(10) The palmaris longus and its homologue in the leg, the 

 plantaris, are vestigial, aberrant in form, and often absent. The 

 plantar and palmar fasciae represent their divorced tendons. 

 The plantaris and palmaris undergo retrograde changes in the 

 Primates with the transformation of claws to nails. 



(11) Each digit (fingers and toes) in lower Primates, such as 

 monkeys, is provided with three short muscles which arose from 

 the carpus or tarsus. The three muscles are (Pig. 250): (1) a 

 short flexor on the radial side of the digit ; (2) a short flexor 



