270 MB. F. G. PARSONS ON THE [Mar. 20, 



Ed-tensor Carpi Ulnaris. — Tliis muscle possessed the same 

 attachments as in Man wnth the exception of Sphingurus, in which 

 the insertion had worked round to the palmar surface of the 

 base of the fifth metacarpal bone. 



Supinator Brevis. — This muscle rises from the external condyle, 

 and is inserted into the upper third of the extensor surface of the 

 radius, wrapping round that bone very little. It only consists of 

 one layer, which lies entirely superficial to the posterior inter- 

 osseous nerve. 



Extensor Ossis Metacarpi Pollicis. — This muscle, which is 

 generally well developed, rises from the extensor surfaces of the 

 radius and ulna, or of the ulna alone, and from the interosseous 

 membrane ; its insertion is into the base of the first metacarpal 

 bone and sometimes into the trapezium. In Hijstrix the insertion 

 is into the metacarpal bone and trapezium. In Cavia cohaya the 

 insertion is into the trapezium, but in Mivart and Murie's case it 

 also sent a slip to the base of the second metacarpal '. In the 

 Sciuromorpha except Castor it rises from the ulna only. In Castor 

 the muscle was double : the first part rose from the radius and 

 was inserted iuto the first metacarpal, while the second rose 

 from the radius and ulna and was inserted into the radial sesamoid 

 bone of the palm. 



Extensor Primi Internodii Pollicis. — This muscle was absent in 

 all the animals examined. Meckel suggests that it may be incor- 

 porated with the extensor ossis metacarpi. 



Extensor Secundi Internodii Pollicis. — This muscle was only 

 found in Hystrix and Castor ; in the former it arose from the ulna 

 below the extensor ossis metacarpi, and was inserted by a thiu 

 tendon into the terminal phalanx of the first digit. In Castor it 

 rises from the upper part of the dorsal surface of the ulna in 

 common with the extensor indicis ; it is inserted into the thumb 

 as in Bi/strix, but sends a slip to the common tendon on the 

 dorsum of the index. 



Extensor Indicis. — The extensor indicis rises from the dorsal 

 surface of the ulna about its middle, and joins the tendon of the 

 extensor communis digitorum on the dorsum of the index. In 

 Hystrix a small slip was noticed, which ran down to lose itself on 

 the dorsum of the fourth metacarpal bone. In Castor the muscle is 

 blended with the extensor primi internodii as above stated. 



Palmaris Brevis.— This muscle is usually well marked and is 

 attached to the pisiform bone and skin on the inner side of the 

 palm ; from this it runs transversely across to the radial side, being 

 interrupted by the palmar cartilage or cartilages to which it is 

 attached. In the Dipodidae, in which a transverse bar of bone 

 runs across the palm, it is very slightly marked. 



In Caproniys melanurus Dobson ^ describes it as sending a slip 

 to act as the flexor perforatus of the Httle finger ; this sHp is what 

 I describe, after Mivart and Murie, as flexor brevis manus. 



ip.Z. S. 1866, p. 383. 

 " P. Z. S. 1884, p. 234. 



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