1891.] DOLICHOTIS PATAGONICA. 241 



condyle of the humerus, one of them (the more superficial) being 

 much larger than the other. The two remaining heads arise 

 respectively from the radius and ulna. 



The Extensor metacarpi radialis is a large muscle, the largest of 

 tlie extensors ; its tendon is inserted on to outer side of metacarpal 

 of 3rd digit, having previously given off a slip to the head of the 

 first metacarpal {i. e. that of 2nd digit). 



The Extensor communis digitorum arises not only from the 

 external condyle of the humerus, but also by a few fibres from the 

 ulna ; its tendon splits at the wrist into four tendons supplying the 

 four digits. 



The Extensor minimi digiti is the smallest of the three upper 

 extensors ; it arises from extensor condyle and from ulna ; it supplies 

 4th and 5th digits. 



The Extensor carpi ulnaris calls for no special remark ; it is as 

 in the Agouti. 



These are all the extensors of the manus of Dolichotis. 



Muscles of the Hind Limb. 



The Gracilis consists of two distinct parts as in other Rodents. 

 One part of the gracilis is sometimes spoken of as sartorius ; the 

 muscle is inserted on to fascia covering leg from knee to ankle- 

 joint ; it also appears to have a tendinous connection with both the 

 semimembranosus and semitendinosus. 



The Semitendinosus is a strong and fleshy muscle ; it arises from 

 the spines of the sacral vertebrae and from the tuberosity of the 

 ischium ; it is inserted by a moderately broad flat tendon, which 

 becomes thicker at its insertion to outside of cnemial crest of tibia. 



The Biceps has two origins — (1) from sacral vertebrae in front of 

 the semitendinosus and continuous with it; (2) from tuberosity of 

 ischium, also in front of semitendinosus. It is inserted by a continuous 

 broad sheet of muscle on to fascia covering leg. 



The Tibialis anticus arises by two heads — (1) by a long tendon from 

 the femur which passes beneath the patello-tibial ligament ; (2) by a 

 fleshy head from tibia and fibula. The two parts are blended a short 

 way down and inserted by a strong tendon on to inner side of inner 

 metacarpal. 



The Extensor communis arises by a long tendon from the femur ; 

 its tendon of insertion passes under two annular ligaments, one at 

 ankle-joint through which the tendon of the tibialis anticus also 

 passes, and another near the proximal end of the metacarpal ; just 

 before passing through the second annular ligament the tendon splits 

 into two ; each of these again splits into two ; the two outer of the 

 four tendons supply the two outer digits ; the two inner ones both 

 go to the middle digit. 



The Extensor hallucis is a slender muscle arising from the tibia 

 and fibula ; its tendon does not pass through the lower annular 

 ligament ; it supphes the second digit. 



The Extensor brevis is a small flat triangular muscle, two tendons 

 arise together from the muscle and supply the two inner digits. 



Proc. ZooL. Soc— 1891, No. XVI. IG 



