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



the external plantar nerve run superficial to it points to its real nature. It arises from 

 the under surface of the os calcis and from the calcaneo-cuboid ligament, and is inserted 

 into the inner sesamoid bone of the minimus. 



Dorsal layer. — This layer is composed of a strongly developed abductor minimi digiti, 

 and the vestige of an abductor ossis metatarsi minimi digiti. 



The abductor minimi digiti (cl 6 ) is the largest of all the intrinsic muscles, and it has 

 an unusual plantar position on account of the minimus being pushed inwards so as to 

 lie in a plane posterior to the annularis. It arises from the under and anterior aspect 

 of the tuber of the os calcis, and is inserted into the outer sesamoid of the minimus. 



Abductor ossis metatarsi minimi digiti. — On the outer surface of the os calcis there is 

 a dense fibrous band containing a number of muscular fibres ; these do not extend so far 

 forward as the fifth metatarsal bone. There can be Httle doubt but that they represent 

 this muscle. 



In the fcetus I examined the hallux was destitute of intrinsic muscles. In the 

 specimen dissected by Miall and Greenwood there was a small flexor brevis hallucis. 



Nerve-supply of the intrinsic muscles. — As in the case of the hyrax the internal 

 plantar nerve (i.p.n) gives off a deep branch. This proceeds from the digital nerve, which 

 divides to supply the contiguous sides of the medius and index. It is a twig of some 

 size, and sinks into the sole to supply both heads of the flexor brevis indicis, and effect 

 a junction with one of the deep branches of the external plantar nerve. 



The external plantar nerve (e.p.n) sends off three deep branches which break up to 

 supply the flexor brevis medii, the flexor brevis annularis, and the flexor brevis minimi 

 digiti. The lowest of these twigs hooks round the transversus indicis, and supplying it 

 with one or two small filaments communicates with the deep branch of the internal 

 plantar. The abductor minimi digiti draws its nerve-supply direct from the trunk of 

 the external plantar nerve. 



Rodentia. 



Lepus timidus (Hare), (PI. XL fig. 10). 



The four outer toes of this foot are well developed, but the hallux is absent. The 

 intrinsic muscles are so completely plantar in position that they are quite invisible from 

 the dorsal aspect of the foot. The dorsal layer of muscles is not represented in this foot, 

 and the plantar muscles are very feebly developed, and are evidently undergoing 

 retrograde changes. 



Plantar layer. — Two very minute muscular slips are the only representatives of this 

 layer. They are (l) the adductor minimi digiti (p 5 ), and (2) the adductor indicis 1 (p 2 ). 



1 St. George Mivart and Murie, in speaking of the intrinsic muscles in the foot of the Hare, Jo not mention these 

 adducting muscles. (Anatomy of the Crested Agonti, Proc. Zool. Soc, 1866, p. 415). 



