1897.] NATURAL SCIENCES OF PHILADELPHIA. 45 



The radial carpal extensors are inserted upon the radial side of 

 the base of their respective metacarpal bones. These facts are sig- 

 nificant since they point to flexion of hand or forearm, while the 

 latter is semi prone, which is the position proved by the study of 

 joints to be characteristic. 



The Extensor carpi radialis longior goes with the Supinator longus 

 since the two are united, and the Extensor carpi radialis brevoir goes 

 with the Extensor communis digitorum, but the Extensor carpi 

 ulnaris does not go with the Extensor minimi digiti in the sense that 

 the two are united. 



The Extensor communis digitorum. — This muscle is the more super- 

 ficial of the two extensors. It does not supply the first finger. It 

 is composed of two slips which separate at the proximal third of 

 the forearm and are far apart at the wrist ; the inner (radial) passes 

 to the second, third, fourth and fifth fingers, and the outer (ulnar) 

 to the fourth and fifth. Thus the fourth and fifth fingers are doubly 

 supplied. Burmeister separates the last named divisions Under the 

 name of the Extensor digiti quarti et quinti, but the remaining part 

 is not the Extensor digiti indicis et medii unless we accept this fasci- 

 cle as having a wider range of insertion than is normal to T. tar- 

 sius. 



Assuming that all the extensors (excepting those of the first fin- 

 ger) described by Burmeister are embraced in the above account, a 

 large muscle in the Academy's specimen remains undescribed. This 

 muscle which is analogous to the Flexor profundus digitorum is 

 much smaller than the Extensor communis. It arises from both 

 bones of the forearm but not from the humerus, and is inserted into 

 all five fingers. The tendon to the first finger is given off high up, 

 but unites with an aponeurotic layer which holds together the ten- 

 dons to the second, third and fourth fingers. The tendon to the fifth 

 finger is next longest to the first and is without aponeurosis. 



The Extensor communis digitorum sends a slip high up from the 

 belly ; it passes through a separate sheath at the wrist (at the head 

 of ulna) and goes to the fourth and the fifth digits. This probably 

 is the Extensor minimi digiti. The main muscle is distributed to all 

 the digits. 



The Extensor minimi digiti arises entirely from the ulna and sup- 

 plies all the digits. Hence the fifth digit receives three extensor 

 tendons. 



The Extensor pollicis longus. — This muscle is normal to T. tarsius. 

 It is the same as the Abductor pollicis longus of Burmeister. 



