492 The Phylogeny of the Palmar Musculature 
In 1887 Flemming reconsidered the question as to the proper signifi- 
cance of the various parts of Albinus’ muscle and arrived at a conclusion 
somewhat similar to that of Cruveilhier, namely, that the term flexor 
brevis should be applied to the outer head only, the entire inner head 
being regarded as a portion of the adductor. To this view Cunningham 
(1887), on the basis of his earlier work (1878 and 1882), took excep- 
tion. As already pointed out, he appled the term flexor brevis to the 
muscles constituting his intermediate layer and regarded each of these 
muscles as being typically two-headed. Accordingly, while admitting 
the correctness of the reference of the entire inner head of the flexor brevis 
pollicis of Albinus to the adductor, he maintained that the true flexor 
brevis was represented not only by the so-called outer head but also by 
the interosseus primus volaris of Henle, these two slips constituting the 
radial and ulnar heads, respectively, of the pollical portion of the inter- 
mediate layer. This same view he had already advanced in an earlier 
paper (1882s), and it is that presented by Patterson in the recently 
published text-book edited by Cunningham (1902). 
segenbaur in his Lehrbuch der Anatomie (5th Ed., 1892) adopts 
essentially the view of Flemming and Cruveilhier, but in a paper pub- 
lished in 1889 he takes the position that the variation in the nerve sup- 
ply of the muscle described by Brooks (1886) indicates that the muscle 
is a variable one and is not equivalent in all cases, portions of it present 
in one individual as indicated by the nerve supply being absent or 
replaced by portions of other muscles in other individuals. 
There is thus a very considerable amount of difference in the limita- 
tions set to the muscle by different authorities. I believe, for reasons 
that have already been set forth in speaking of the flexor brevis quinti 
digiti, that the term flexor brevis pollicis should be reserved for that 
portion of the muscle as described by Albinus which is derived from the 
flexor brevis superficialis, and the portion which has that origin is the 
so-called outer head. Cunningham is, I believe, in error in referring 
this head to his intermediate layer; it seems to me clearly equivalent to 
the flexor brevis pollicis of the mouse, for instance, and this is undoubt- 
edly a derivative of the flexor brevis superficialis, as is shown as well by 
its origin as from its supply by the median nerve. 
On this point, then, my results are in accord with those of Flemming, 
and I am in agreement both with that author and with Cunningham in 
regarding the inner head as a portion of the adductor. What, then, is 
the interosseus primus volaris of Henle? Why, it is evidently just what 
Henle named it; it is the equivalent in man of the slip of the flexor 
brevis profundus which arises from the first metacarpal and inserts 
