MYOLOGT OF THE ORNITHORHYlSrCHUS. 165 



Gracilis. Of great size. Arises fleshy, in apposition with, its fellow 

 for the whole length of the symphysis pubis, and greater part of 

 outer surface of marsupial bone. Above, it is connected with the 

 symphyseal aponeurosis of the obliquus externus abdominis ; below, 

 with a slight tendinous intersection, it sends straight backward the 

 peculiar slip that goes to the cloaca. The muscle passes nearly trans- 

 versely outwards, overlying all the other tibial flexors as well as the 

 femoral adductors. Its posterior border is curved and somewhat 

 tucked under, while the anterior border is straight ; the muscle con- 

 verges and grows at the same time thinner, to be inserted by a short, 

 flat, broad tendon into the shaft of the tibia, for half an inch along 

 the middle third of the bone. Primarily, the gracilis is a strong direct 

 adductor of the whole limb ; next it flexes the tibia, and finally ro- 

 tates the leg inward. 



Semitendinosus and Semimembranosus have continuous origins and 

 insertions, parallel and contiguous courses, and similar functions : 

 neither displays the physical structure that led some one to encumber 

 anatomy with two of the most unhandy and inept names in the sci- 

 ence. Both are direct flexors of the leg, and extensors of the whole 

 limb, with a little inwardly rotating action. The one-half membrano- 

 sus is the posterior of the two ; it has definite origin from the tip of 

 the ischium next to the biceps ; is of a flattened terete shape, taking 

 straight course to the leg, where it has extensive fleshy insertion for 

 half an inch along the upper third of the tibia, just to one side of 

 its crest. The one-half tendinosus, has more extensive and chiefly 

 tendinous, but also partly fleshy origin from the ascending ramus of 

 the ischium, between the origin of the foregoing and that of the adduc- 

 tor. It forms a prismatic muscle, owing to its flat under and super- 

 ficial, and bevelled posterior, aspects; the one-half membranosus 

 resting on the latter. It converges abruptly to a point, with definite 

 tendinous insertion into the head of the tibia, at the most internal and 

 projecting point of the latter. 



Sartorius. Here its true office as an extensor cruris and flexor fem- 

 oris is contravened, and we find the muscle, much as in man, at 

 once a flexor of two consecutive segments. Its low, instead of high, 

 pelvic, or even vertebral, origin has been already mentioned. It 

 arises from the apex of the pectinseal eminence, in connection with 

 the insertion of the psoas parvus, by a round cord-like tendon ; passes 

 outward upon the inner aspect of the limb, overlying pectinaeus and 

 adductors, expanding remarkably as it goes, into a flattened, triangu- 

 lar muscle. Narrowing somewhat, it becomes aponeurotic just below 

 the internal condyle of the femur, and is attached to the naked space 

 in front of the tibia above, though really continuous with the some- 

 what similar fascial expansion of the biceps. It is, firstly, an adduc- 



