12 PROCEEDINGS OF THE NATIONAL MUSEUM vol.80 



the tendon of the short biceps may usually separate quite high up at 

 times (as in Pithecus)^ with some of the biceps fibers arising from 

 the coracobrachialis tendon below the point of separation. More 

 rarely the fission does not occur until quite at the middle of the 

 brachium (as in Galago). 



Usually there is fusion of the long and short heads of the biceps, 

 most frequently at about the middle of the brachium or a bit below 

 (as in Pan. Papio^ PygatJirix^ Gebus^ Aotits, and Perodicticus)^ or 

 occasionally this does not take place until within a short distance 

 of the insertion (as in Pithecus, Lasiopyga^ and Ateles). and rarely 

 the two heads are entirely separate throughout their length (as in 

 Tarsius and Didelphis). In man the two heads of the biceps usu- 

 ally fuse well above the tendon, but at least in some of those cases in 

 which the two are separable as far as the tendon it is easily demon- 

 strable that both heads are concerned with the formation of the 

 radial bicipital tendon, 



^Yliereas insertion of the longer biceps is invariably on bone, that 

 of the shorter head is more variable, going in some cases to the 

 radius, to the ulna, or having a variety of fascial attachments. The 

 best known of the latter is represented by the lacertus fibrosus or 

 semilunar fascia as of man. This takes the form of a tough fascial 

 connection between chiefly the short biceps and the medial anti- 

 brachium, concerned with certain of the antibrachial flexors. This 

 we liave found to be indubitably present in such primates as Pan, 

 Ateles, Aohas (2 specimens), and Galago; absent in Hylohafes, 

 PygatliTix, Papio, Plthecus, Lagtopyga, Gebus (2 specimens), 

 Sahniri, Nycticehus, Perodicticus, and Tarsius (2 specimens) . From 

 the condition typical of man there are found several fascial 

 variations. In Galago, for instance, we found that there was not 

 only a superficial lacertus as well as tendinous attachment of the 

 short head to the radial insertion of the longum but in addition a 

 fascial band that was intermediate in position between the other two 

 and that passed deep between the pronator teres and flexor carpi 

 radialis, probably operating directly upon the ulna by means of the 

 intermuscular septum. On the other hand, in Hylohates lar the 

 shorter biceps head, analogous and possibly homologous to the usual 

 caput breve, diverged from the common biceps mass to fuse com- 

 pletely with the substance of the flexor digitorum sublimis, the fibers 

 of the two being perfectly continuous and acting in some respects as 

 a single muscle extending from shoulder to digits. It is easy to see 

 how such a situation could have developed from a lacertus, or how 

 insertion by means of the latter could shift to intermuscular septa 

 and so reach the bone. 



