86 THE VOYAGE OF H.M.S. CHALLENGER. 



latter towards the index. The flexores breves of the medius and annularis which are 

 merely represented by tibial heads act no doubt like the first and second plantar inter- 

 ossei in man by antagonising the action of the third and fourth dorsal interossei. The 

 index presents the anomaly of being provided with four intrinsic muscles, viz., (1) an 

 adductor, (2) the tibial head of a flexor brevis (antagonistic to the adductor), and (3) two 

 dorsal interossei (antagonistic to each other). So far as I am aware, this disposition of 

 muscles is quite unique. 



In Cuvier and Laurillard's plates l the abductor and the flexor brevis hallucis are alone 

 figured (pi. cclxiii. fig. 1). 



Rapp 2 merely describes the abductor minimi digiti, and states that the interossei lie 

 in the intervals between the toes. 



From a careful study of the account given by Professor Humphry 3 of the intrinsic 

 muscles in the foot of the Manis (Manis dalmani), it seems to me that in their arrange- 

 ment they closely resemble those of the Tamandua. Thus the plantar layer is composed 

 of — (1) an adductor hallucis, (2) an adductor minimi digiti, (3) an adductor iudicis, and 

 (4) a transversus indicis, all of which are inserted in a similar manner to the corresponding 

 muscles in Tamandua. These muscles Professor Humphry terms plantar interossei, and 

 he classes with them two additional muscles, which he remarks are " situated on rather a 

 deeper plane, nearer to the metatarsals, and pass, one to the fibular side of digit 3, and 

 one to the fibular side of digit 4." These latter appear to me to be the fibular heads of 

 the flexor brevis medii and flexor brevis annularis. With regard to the intermediate 

 flexores breves it is evident that he includes three members of this group amongst the 

 dorsal interossei, viz., the tibial head of the flexor brevis medii, the tibial head of the 

 flexor brevis annularis, and the tibial head of the flexor brevis minimi digiti. This layer 

 therefore, consists of — (1) a tibial head of the flexor brevis hallucis, (2) a two-headed flexor 

 brevis medii, (3) a two-headed flexor brevis annularis, and (4) a two-headed flexor brevis 

 minimi digiti. The dorsal layer thus reduced will consist of the same component parts as 

 the corresponding layer in Tamandua, with the exception of the abductor ossis metatarsi 

 minimi digiti, which is absent in Manis. Further, these muscles are inserted so as to 

 abduct from a line drawn through the index. 



The only essential difference between the intrinsic muscles in the foot of the 

 Tamandua and of the Manis would appear to be in the disposition of the flexores breves. 

 In the former each digit is supplied with a short flexor, but in the case of the minimus 

 alone is this muscle two-headed ; in the Manis the index has no flexor brevis, and the 

 flexor brevis medii, the flexor brevis minimi digiti, and flexor brevis annularis are two- 

 headed. 



1 Anatonrie Comparee Recueil de Planches de Myologie. 

 - Anatomische Untersuchungen uber die Edentata. 



5 The Myology of the Limbs of the Unau, the Ai, the two-toed Ant-eater, and the Pangolin, Jour. Anat. and Phys., 

 vol. iv. 



