16 PROCEEDINGS OF THE NATIONAL MUSEUM vol.80 



flexor digitorum sublimis. He indicated that such an arrangement 

 is important to the gibbons in making their tremendous leaps from 

 branch to branch. 



This curious-and apparently unique specialization of the brachial 

 flexors in the gibbon appears to us more as a secondary adaptation 

 of purely functional significance, and we are of the opinion that little 

 or no phylogenetic import should be attached to it. In this view we 

 disagree completely with Gronroos, who concluded that the three 

 great apes, the gibbons, and man all passed through a stage in which 

 the biceps brachii possessed three heads — supraglenoid, coracoid, and 

 tuberculoseptal. His ingenious theory, based chiefly upon the posi- 

 tions of supernumerary humeral biceps heads (which he regarded as 

 remnants of the caput tuberculoseptale) appears to us as unconvinc- 

 ing, for consideration of the biceps morphology in the various groups 

 of primates does not lend support to his views. 



Mention should also be made of other theories concerning the 

 phylogeny of the biceps. Humphry (1872) homologized the two 

 heads of the biceps of man with the entire coracoradialis (caput 

 longum) and the outer portion of the coracobrachialis longus (caput 

 breve) of the urodele amphibian Cryptohranchus japonicus. Welcker 

 (1878) found that in some mammals (as the tapir) the tendon of 

 the caput longum lay outside of the capsule. In other forms the 

 tendon exhibited various degrees of encapsulation. He likewise 

 found a gradual ontogenetic migration within the capsule occurring 

 in some forms (beaver, Cebu^, man), and therefore came to the 

 conclusion that the tendon of the caput longum has secondarily 

 migrated within the capsule of the shoulder joint. This supports 

 other comparative evidence that indicates that the supraglenoid 

 origin of the long head is a relatively late phylogenetic acquisition. 

 Fiirbringer (1876) was inclined to the view that the caput longum is 

 homologous with the entire coraco-antibrachialis of reptiles, the 

 caput breve being derived from the coracobrachialis. Eisler (1895) 

 secondarily derived the caput breve from both the coracoradialis and 

 coracobrachialis longus of urodele amphibians. He did not definitely 

 commit himself in respect to the caput longum, but listed three possi- 

 ble explanations: (1) It is a part of the coracoradialis proprius, 

 which has gained attachment to the scapula; or (2) it is a part of the 

 caput breve, which has become attached to the ligamentum humero- 

 radiale (sive capsuloradiale), which is itself the degenerated tendon 

 of the original coracoradialis proprius; or (3) it represents a com- 

 bination of the two preceding processes. Lubosch (1899) regarded 

 the caput longum as a derivative of the accessory or humeral head of 

 the coraco-antibrachialis of reptiles. 



