THE SKELETON IN THE FLYING LEMURS. 195 



come next in length and nearly equal each other in this respect. Medius 

 and annulus metacarpals are also of equal length and larger than any of 

 the other bones of this part of the hand. Pollex metacarpal is the stoutest 

 of them all and is about 1.6 centimeters long; minimus is also stout and 

 has a length of about 2.8 centimeters, while that of index is 5 millimeters 

 shorter. The shafts of the middle and ring, or the medius and annulus, 

 metacarpals are rather more slender, and each is nearly 3 centimeters long. 

 These metacarpal bones are slightly curved palmad and like the phalanges, 

 nearly parallel and very close to each other vi^hen the member is at rest. 

 Pollex has one short (1.5 centimeters), stout phalangeal joint and an 

 ungual joint; all the other digits have three each including the ungual 

 joints. Index is the shortest finger, minimus next, with medius and 

 annulus of about equal length. Not including the terminal joint, annulus 

 has a length of about 4 centimeters. 



The ungual joints are all very much of the same form and size ; the 

 largest being on pollex, index, and the next two digits, the smallest on 

 the little finger. Any one of th-em is very deep from dorsal to pahnav 

 border, the latter being slightly concave, and the former powerfully con- 

 vex and a little jagged distally. From side to side one of these thoroughly 

 ossified joints is uniformly compressed to extreme thinness, while its 

 proximal border is somewhat thickened for the articular facet and for 

 tendinal insertions. At the postero-dorsal angle there is a very small, 

 concave, circular process for the insertion of the extensor tendon ; palmad 

 to this is a large concave facet divided by a median longitudinal ridge. 

 This concavity is twice as deep as it is wide, and its surrounding border is 

 raised above the general surface. Palmad to this again, at the postero- 

 palmar angle, there is another very small process for the insertion of 

 the flexor tendon, while above this, beneath the lower border of the mid- 

 articular facet, are two minute foramina, side by side in the transverse 

 line. They lead into the bone and appear to be nutrient foramina. 



The horny theca, fitting as a, claw over one of these ungual joints, is 

 also powerfully compressed from side to side, and in form, with its very 

 sharp apex, resembles upon lateral view the upper bill of one of the 

 smaller typical falcons. 



On the palmar aspect, beneath the articular joints of the metacarpals 

 and phalangeal bones, we observe in the case of each digit a pair of se- 

 samoids. These have the form of small compressed ellipsoids, the largest 

 ones being in the proximal tier of bones, whereas in the case of the 

 smaller pairs beyond, they are placed side by side in the transverse line. 



Distally, the sesamoids are very minute and may be absent in the 

 index digit, between its first and second phalanx. They do not occur, 

 apparently, beneath the ungual joints at all. These sesamoids occur in 

 the hands and feet of other mammals, as certain carnivora, and even 

 in the tendons running to the toes on the plantar aspect of the foot in man. 



