172 un. F. G. PAIiSONS ON THE [Juii. 14, 



found is that the outer division of his extensor carpi ulnaris is 

 really the extensor minimi digiti, the tendon of which has lost its 

 digital attachments and has become inserted into the base of the 

 fourth metacarpal bone. 



Supinator iJreww.— The description of this muscle given in the 

 other Eodents applies to the Myomorpha, with the exception that 

 in the latter a sesamoid bone is usually found in the tendon. 

 The only animals in which this bone was wanting were Baihyenjus 

 and Oeoryclius. The relationship of the tendon of the supinator 

 brevis to the external lateral ligament of the elbow is interesting, 

 in some cases, as in that of Bathyergvs, there is a well-mai-ked 

 external lateral ligament, situated behind the tendon, but in 

 others, of which Cricetomys is an example, the tendon itself seems 

 to form the lateral ligament, and has the orbicular ligament 

 attached to it. 



Extensor Ossis Metacarpl PulUds. — In all cases this muscle rises 

 from both bones, and is inserted into the base of the metacarpal 

 bone. In the Gerbille its tendon was double. In Gricetus and 

 Cricetomys it had an extra insertion into the radial sesamoid bone 

 or palmar cartilage. 



Extensor Primi Internodii FoUicis, — In every animal examii>ed 

 this was absent. 



Extensor Secundi Internodii I'olUcis. — This muscle was only seen 

 in Qeorychus, where it was well-marked, it accompanied the 

 extensor indicis and separated on the back of the hand. This 

 arrangement is practically the same as that already described in 

 Castor. 



Extensor Indicis. — As in other Eodents the extensor indicis 

 rises from about the middle of the back of the ulna, and is inserted 

 only into the dorsal side of the index. In Ilyoxus it rises from 

 the top of the back of the ulna close to the olecranon. In the 

 Vole 1 dissected the tendon had acquired a secondary attachment 

 to the prominent ridge on the back of the radius at its lower end, 

 while the part of the tendon between this and the index was 

 wanting. 



Palmaris Brevis. — When a palmar ossicle is present, which is 

 not so often the case as in other Eodents, the muscle is attached 

 to it. "When there is no ossicle it is attached to the palmar fascia. 

 In Microtvs and Bathyergus no palmaris brevis was found. 



Plexor Brevis Digitorum Manus. — This muscle was found in 

 Cricetomys, Cricetus, GeorycTiits, and Bathyergus. In the first three 

 it arose from the palmar ossicle, but in the last from the fascia 

 just external to tlie pisiform bone. 



Muscles of iTie Thumb. — In almost all cases the abductor pollicis 

 can be made out, and has its origin from the palmar ossicle. The 

 flexor brevis was made out with difficulty in Myoxus, Qeorychus, 

 and Bathyergus ; in the two latter the thumb is provided with a 

 pair of sesamoid bones, as in all the other fingers, Bathyergus 

 has a prominent cartilaginous spur on the outer and inner side of 

 the hand; these probably represent the prepoUex and post minimus. 



