MYOLOGY OF THE ORNITHORHYNCHUS. 167 



relations, and more nearly resembling in its attachments, course and 

 function, the " interosseus cruris" of some animals, which is not de- 

 veloped in the present instance. 



This muscle is decidedly not to be referred to the pronator radii 

 teres. 



c. Acting upon tarso-metatarsus from femur or leg, or both. 



The great size of the spoon-shaped peronecranon, from which nearly 

 all the muscles of the foot arise, either wholly or in part, effects (a) 

 greater power of such muscles, in consequence of actual increase of 

 contractile mass, (&) advantageous rotatory operation, and (c) a very 

 peculiarly shaped calf. On the front and outer side of the leg, the 

 muscles rather suddenly contract to tendons at about the middle ; 

 those behind run nearly to the heel ; all are very closely packed above, 

 while below, the tendons are much separated by intervention of fascial 

 and adipose tissue. 



We may note, at the outset, that " peroneus tertius " occurs here in 

 its true character of extensor minimi digiti pedis a common, if not 

 the customary condition of the muscle in animals below the highest ; 

 our notion of its antitypic relations with a muscle of the fore limb is 

 given further on. The digital extensor set is double in the leg ; i. e., 

 the deep set, that in man, etc., is restricted to the instep, here runs up 

 the leg. In some marsupials, e.g., opossum, the same muscle is 

 peroneal, and deflects behind the malleolus externus before distribu- 

 ting its tendons to the digits. Here it comes directly down the front 

 of the leg and is clearly displayed as one of the true digital extensors, 

 corresponding to the special extensores pollicis and indicis, in the 

 hand. Extensor longus hallucis is present and of usual characters. 



Flexor tarsi tibialis; h. e., TiUalis anticus.The innermost muscle 

 upon the front of the leg; large; superficial; arising by two heads. 

 The smaller of these takes fleshy origin from the tibial shaft in front, 

 from its head half way down ; and is divided by a cellular interspace 

 from the other, the larger, head which arises from the patella and a 

 corner of the peronecranon in apposition with the extensor hallucis. 

 The two join and become tendinous at the middle of the leg ; the stout 

 tendon passes in front of the inner malleolus, most internal of any, 

 to its customary insertion into the base of the first metatarsal. The 

 usual action. 



Extensor tarsi tibialis; h. e., Tibialis posticus. A large, very deep- 

 seated muscle upon the back of the leg, filling the wide interrosseus 

 space, but having no tibial origin. It consists essentially of two 

 parts ; the shorter and thicker of these arises from the articular head 

 of the fibula, and a ridge thence two-thirds way down the tibial as- 

 pect of that bone ; the longer and thinner part from the back of the 

 shaft of the fibula and most of the posterior surface of the perone- 



COMMUNICATIONS ESSEX INSTITUTE, VOL. VI. 22 April, 1871. 



