316 Dr. A. Macalister on the Formation of 
dified in several singular ways. As we saw that its antithesis, 
the extensor, was sometimes inserted, not into the bones di- 
rectly, but into the common extensor tendon, so we usually 
see, as in the human pes, part of this flexor arising from the 
first row of the tarsus, and inserted, as the musculus acces- 
sorius, into the tendon of the flexor digitorum longus. And 
as, from the hyperdevelopment of the calcaneum, the latter 
tendon is forced to run obliquely to its insertion in the human 
and some other pedes, so this muscle is adapted in such cases 
to fulfil the special function of obviating what would otherwise 
be the faulty direction of the long tendon, and altering its line 
of action into one of greater convenience: for this purpose the 
muscle is shortened, or at least its belly is tacked on to the 
flexor tendons near to the ankle. But the muscle does not 
terminate here; for, separated from the typical origin by the 
tendons to which the latter has intent an adhesion, the 
continued slips of insertion sink into the interspaces of the 
tendons, and thence are inserted into the fingers under the 
name of lumbricales. Within the present session I have 
seen several distinct examples of the continuity which some- 
times subsists in the human foot between the lumbricales and 
the massa carnea accessoria. In other animals we find the 
musculus accessorius, varied to a slight extent in direction: it 
is present in Ateles, Cebus, and other monkeys. This massa 
carnea Sylvii, however, is not all of this short flexor; there 
is one slip which usually preserves its natural connexions— 
the superficial head of the flexor brevis pollicis manus. It is 
a typical portion of the muscle, arising from the carpus and 
inserted into the first phalanx of the pollex through the inter- 
vention of the outer sesamoid bone; and this leads us to the con- 
sideration of this muscle as developed in the manus. In Hyrax 
capensis, according to Drs. Mivart and Murie (Proc. Zool. Soc. 
1865, p. 341), the muscle is present-as a flexor brevis digitorum 
manus, sending slips to the second, fourth, and fifth digits, the 
slips arising by a large muscular belly in the vicinity of the 
palmar cartilage; in this case the muscle is developed typi- 
cally. It may seem as an & prior? difficulty that this animal 
has two lumbricales (although Meckel denies their existence) 
as well as the large typical flexor ; but this in reality can easily 
be understood, as the former are but deeper and differentiated 
slips of the muscle, just as in the antagonistic foot-muscle, the 
extensor brevis, I found on a recent occasion two tendons, dis- 
tributed one to the outer and the other to the inner side of the 
second toe, all the others being regular. The lumbricales de- 
scribed by the above authors in Hyrax are distributed to the 
second and fourth toes in the fore limb, but to the second and 
