16 ANATOMY OF VERTEBRATES. 



attachments the pronator quadratus of tlic fore limb : it is most 

 developed in the pedimanous climbing Marsupials, where the 

 rotation of the foot is more frequent and extensive. 



Fig. 5 shows this modification of the muscles of the hind-foot in 

 the Phalangista vulpina ; a, is the expanded tendon of the sartorius ; 

 byffracilis', c, seinitcndinosus ; and d, semimembranosus ; both these 

 muscles are inserted, as in many other quadrupeds, low down the 

 tibia : c, gastrocnemius ; f, plantaris ; g, the homologue of the 

 flexor lone/us pollicis pedis ; h, tibialis posticus ; this muscle divides 

 and is inserted by two tendons, h' and h" , into the internal and 

 middle cuneiform bones ; /, the rotator muscle of the tibia. 



In the muscles on the anterior part of the leg, the extensor 

 brevis diyitorum has its origin extended into this region, and is 

 attached to the outside of the fibula. There are three peronei\ 

 the external one is inserted into the proximal end of the fifth 

 metatarsal : the tendon of the middle peroneus crosses the sole in 

 a groove of the cuboid like the peroneus longus : the internal 

 peroneus is an extensor of the outer or fifth toe. The Perameles 

 layotis, among the saltatorial Marsupials, presents a different 

 condition of the extensors of the foot from that above described. 

 The yastrocnemii, soleus, and plantaris all arise above the knee- 

 joint, and the tendon of the plantaris, after sheathing the tendo 

 Achillis and traversing the long sole, is finally inserted into the 

 base of the metatarsal bone of the fourth or largest toe ; thus 

 this muscle, which is strongly developed, bends both this toe and 

 the knee, while it extends the foot. 



In the Kangaroo the flexor of the toes rises from the outer 

 tuberosity of the tibia, its fleshy part covers the back of the leg 

 beneath the soleus, the tendon passes to the sole and divides into 

 a large tendon for the principal toe, fig. 211, iv, a smaller tendon 

 for the outer toe, v 9 and a still smaller tendon which goes to the 

 two slender inner toes. The muscle seems to combine the homo- 

 logues of the flexor liallucis and flexor diyitorum, with, perhaps, 

 also that of the tibialis posticus. 



195. Muscles of L,issencephala. -The Rodentia closely re- 

 semble the Marsupialia in their muscular system ; with like 

 modifications according to the absence or presence of clavicles, 

 and to the gradatory, saltatory, scaiisorial, and fossorial move- 

 ments of the species respectively. They have not the marsupial 

 modifications of the cremaster and abdominal muscles, nor the 

 rotatory muscle of the tibia ; but certain Rodents show pecu- 

 liarities of the masseter which will be noticed in connection with 

 the organs of mastication. 



