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 contracted 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 camea 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 

 camea 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 Hi/rax 

 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 a j^rior-i difficulty that this animal 

 has two lumbricales (although Meckel denies their existence) 

 as well as the larg*e 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 



