266 ME. F. G. PAHSOXS OS THE [Mar. 20, 



seems to be developed iu the palmar fascia. In Octodon aud 

 Myopotamus it rises only from the inner side of the olecranon 

 process, while in Castor it comes from both the olecranon and 

 internal condyle. 



In Ccelogenys and Xerus the muscle w"as formed by some of 

 the internal and superficial fibres of the flexor sublimis digitorum : 

 this arrangement corresponds to what Mivart and Marie found 

 in Dasyprocta, though in the specimen of this animal which I 

 dissected the muscle was absent. In Myopotamus the insertion 

 was into the radial and ulnar palmar cartilages. The muscle was 

 not seen in Chinchilla or Sciurus. In Spermophiliis the tendon 

 was broad and fascia-like in its whole length. Apparently this 

 muscle is liable to great individual variation in Eodents as in Man. 



Flexor Sublimis Digitorum. — This muscle rises from the internal 

 condyle in common with part of the flexor profundus ; it divides 

 into slips for the middle phalanges of the 2iid, 3rd, 4th, and 

 usually the 5th digits, which slips are perforated for the passage 

 of the profundus tendons. Just before the perforation there 

 is usually a strong fibrous loop, which passes under the profundus 

 tendon and comes into contact with the sesamoid bones in front 

 of the metacarpo-phalangeal joints ; this is very weU marked in 

 Ccelogenys. 



In the Octodontidse and Dasyproctidse there are only three 

 tendons for the 2nd, 3rd, aud 4th digits. This is also the case 

 in Castor. Mivart and Murie ^ found a slip to the 5th digit in 

 the Agouti on one side but not on the other. In Ccelogenys I 

 met with a more interesting arrangement still ; in it the tendinous 

 loop representing the perforated portion of the tendon was present 

 in the 5th digit on one side, but was entirely unconnected \\'\\h. 

 the flexor sublimis, which sent no slip to this digit. 



Possibly the explanation of these facts may be that the 

 Dasyproctidse show a stage in the gradual suppi-ession of the slip 

 to the 5th digit, a process which is complete in the Octodontidse. 

 In Castor the muscle has an extra origin from the olecranon. 



Flexor Carpi Ulnaris. — This muscle usually rises, as in Man, 

 from the inner side of the olecranon process, from the internal 

 condyle, and, by aponeurosis, from the upper part of the posterior 

 border of the ulna. It is inserted into the pisiform bone. In 

 the Octodontidae aud Dasyproctidae the condylar origin is wanting, 

 as it is also in Castor and SpermopJiilus. 



Flexor Profundus Digitorum. — This muscle, which includes both 

 flexor profundus digitorum and flexor longus pollicis of human 

 anatomy, rises usually by four heads ; two of these come from 

 the internal condyle, one from the flexor surface of the ulna, 

 and the last from the flexor surface of the radius. The muscle 

 usually divides into four tendons for the outer digits, and often 

 gives off a small tendon at right angles to the rest for the pollex. 

 The tendons perforate the flexor sublimis and are inserted into the 

 terminal phalanges of the digits. 



1 P. Z. S. 1866, p. 383. 



