MUSCULAR SYSTEM OF MAMMALIA. 7 



pollicis, 29, the pronator teres, 32, and the flexor carpi radialis, 33, 

 are all remarkable for their strength in the Ornithorhynchus, and 

 are still more powerfully developed in the Echidna. 



The most remarkable muscle on the palmar aspect of the fore 

 arm is the flexor carpi ulnaris, which arises by two separate 

 heads, the longer one from the broad olecranon, the shorter one 

 from the internal condyle of the humerus ; the common tendon 

 is attached to the os pisiforme and the metacarpals of the fourth 

 and fifth digits. 



The psoas magna and iliacus internus form a single muscle, 

 having the usual origins, and inserted by a common tendon into 

 the large internal trochanter. 



The psoas minor is the largest of these muscles. It arises from 

 the sides of five dorsal vertebrae, and its strong tendon is implanted 

 in the remarkably developed ilio-pectineal process. It depresses 

 the pelvis, and with it also the tail and the pelvic extremities. 



The ectogluteus is larger than is usually the case with qua- 

 drupeds ; its insertion extends to the plantar fascia and the 

 bone which supports the spur. The mesogluteus, entogluteus, 

 pectineus, 45, biceps flexor cruris, gracilis, 34, sartorius, 35, rectus 

 femoris, 36, adductor es femoris, 46, semitendinosus, 47, semimem- 

 branosus, vastus externus, offer no notable deviations from the 

 usual structure. A strip of fibres, 49, descends from the gracilis 

 to the sphincter cloacai, H. A muscle, called by Meckel ( flexor 

 accessorius a cauda ad tibiam tendens,' 51, arises from the trans- 

 verse processes of the anterior caudal vertebra?, and converges to 

 be inserted into the tibia. Another peculiar adductor of the leg, 

 which might be termed s intertibialis,' 52, is attached by its ex- 

 tremities to both tibiae ; its fleshy belly passes across the sphincter 

 cloacae, h, and is connected with a strip of the panniculus car- 

 nosus, i. 



The gastrocnemius, 48, derives its largest origin from the pro- 

 duced and expanded head of the fibula, and its smaller belly from 

 the internal femoral condyle ; its tendon is implanted in the cal- 

 caneum. The homotopy between the gastrocnemius and flexor 

 carpi ulnaris is strikingly illustrated in the Ornithorhynchus. 



The soleus arises from the head of the fibula and from a large pro- 

 portion of the tibia ; it is nowhere blended with the gastrocnemius, 

 but is inserted by a thick and short tendon into the astragalus. 



The abductors of the outer digits of both the hand and foot are 

 well developed for the purpose of expanding the web which 

 connects the toes. 



In the figure the following muscles of the leg are shown — viz. 

 37, tibialis anticus, 38, extensor hallucis longus, 39, peroneus longus, 



