18G().] ON THE ANATOMY OF THE CRESTED AGOUTI. 415 



tendon ; but the latter forms mainly the perforating tendons of the 

 third and fourth digits, sending small slips, however, to the larger 

 tendons of the flexor longus digitorum going to the index and fifth 

 digits. 



Tibialis posticus. This muscle in the Guinea-pig is of fair size, 

 and is inserted into the proximal end of the metatarsal of the index : 

 hut in the Agouti it is wonderfully small, consisting of a minute 

 fleshy belly which arises from the back of the tibia, at its upper part ; 

 its extremely delicate tendon passes down behind the internal mal- 

 leolus, and is inserted into the proximal end of the plantar surface 

 of the naviculare. 



Prof. Huxley, in his Hunterian Course of Lectures for 18C5, said 

 that there is no proper tibialis posticus in the Rabbit ; but a muscle 

 arises from the inner and front face of the tibia, and passes through 

 a groove at the inner malleolus, then runs beside the second meta- 

 tarsal and joins the extensor tendon. For this muscle he proposed 

 the name of tibialis secundi. 



Our dissection of the Rabbit corroborates his observation, and we 

 have also found a similar arrangement in the Hare. In this last the 

 muscle comes from the inner surface of the tibia, and has fleshy 

 fibres for a third of the length of the shaft of the bone ; its tendon, 

 which is flat and closely appressed to the periosteum, is with diffi- 

 culty distinguishable from that until it reaches the malleolus. Its 

 insertion on one foot was into the distal end of the first metatarsal 

 of the index or innermost digit ; but in the other foot the tendon 

 bifurcated opposite the distal end of the inner metatarsal bone, the 

 extra smaller-sized tendon passing to the third metatarsal bone at 

 its distal end. 



The lumbricales of the hind foot are at most but two in number. 

 One arises between the tendons going to the third and fourth digits, 

 and is inserted into the peroneal side of the third digit. Another 

 muscle arises from the tibial side of the tendon of the third digit ; 

 but, as it is inserted into the deep surface of the tendon of the plantar 

 portion of the plantaris muscle, this may very probably represent the 

 accessorius which we found so well marked in the foot of Hyrax*. 

 In the Guinea-pig the above muscles are two in number. In the 

 Hare there are three lumbricales — one arising from the tendon going 

 to the third digit, the second from the tendon common to the fourth 

 and fifth digits ; the third comes from the tendons of the fourth and 

 fifth digits, where these bifurcate. 



The interosseous muscles occupy only the plantar surface of the 

 hind foot ; they are so very large in size as to cover deeply the en- 

 tire surface of the sole (fig. 5, In.) ; they are true flexors of the 

 three digits. There are also three pairs in the Guinea-pig ; these 

 lie so closely appressed as to appear but three single muscles. In 

 the Rabbit, as well as in the Hare, there are four pairs of interossei 

 muscles in each foot, corresponding to the number of the metatarsal 

 bones. They arise in common by a very strong fascia from the 

 tarsus, and are inserted respectively into the sesamoid bones on the 



* Lor. rit. p, 351, fig. 13, A. 



