189 



the foot. With this conclusion I agree. The slips B and C are ele- 

 ments of no morphological value and their presence merely indicates 

 a tendency on the part of the radial fibres of B to wander outwards 

 in search of a more extended insertion ^). I cannot, however, agree 

 with his statement that the flexor brevis pollicis is a one-headed 

 muscle and is represented solely by J. — the superficial or radial 

 belly. My investigations into the comparative Anatomy of the intrin- 

 sic muscles and nerves of the mammalian manus et pes^) have taught 

 me to regard the primitive condition of a flexor brevis, whether it be- 

 longs to the pollex or any other of the digits, as being two-headed. 

 Man is no exception to the rule. In a certain proportion of mammals 

 one or other head may fail or be so reduced in size that it requires 

 the greatest care to make it out, but its morphological importance as 

 a distinct muscular element is in this way by no means impaired. In 

 Man the ulnar head of the flexor brevis pollicis has suffered from the 

 great development of the adductor. It has been unable to hold its 

 ground against the latter, and has ultimately been thrust deeply back- 

 wards, so that it can only be exposed satisfactorily by dissecting from 

 the dorsal aspect of the hand. It is the muscle which is termed by 

 Henle •'') the interosseus primus volaris (or the interosseus 

 pollicis indicisque). When the outer head of the first dorsal inter- 

 osseous muscle is carefully reflected this slender slip will be found 

 closely applied to the ulnar side of the metacarpal bone of the thumb, 

 from the base of which it usually takes origin. It is completely covered 

 from the front, by the muscle named B. Henle's figure can hardly 

 be regarded as giving a satisfactory representation of it. I have 

 rarely found the interosseus primus volaris absent in Man, although 

 in the Gorilla and Chimpanzee the relatively great development of 

 the adductor (D) has led to its total extinction *). The struggle 

 between the more powerful adductor and the weaker ulnar head of 

 the flexor brevis can be studied in most of its stages in the hand of 

 the difi"erent apes. 



1) The condition of slip B in the apes has been well described by 

 Dr. Beooks, Journ. of Anat. and Phys. July 1886. 



2) Challenger Reports Part XVI. — Report on some points in the 

 anatomy of the marsupials ; with an account of the comparative anatomy 

 of the intrinsic muscles and the nerves of the mammalian pes. 



3) Handbuch der Anatomie, "Muskellchre", p. 246, Fig. 119. 



4) Beiträge zur Anatomie des Hylobates leuciscus von Professor 

 Dr. J. L. W. V. Bischoff. 



