REPORT ON THE MARSUPIALIA. 37 



process of the first caudal vertebra — on the same plane with the superficial muscle, and 

 undercover of the agitator caudse. It passes downwards under cover of the biceps 

 proper, and appearing at its posterior border is inserted into the fascia on the fibular 

 aspect of the leg. 



These caudal divisions of the biceps muscle are undoubtedly present lor the purpose 

 of associating the movements of the heavy tail with those of the hind limb. 



The bicepiti accessorius appears to be only occasionally present. According to 

 Macalister 1 it is found in Sarcophilus, but "is absent in the Wombat, Giant Kangaroo, 

 Bennett's Kangaroo, Phalanger, and Opossum. Young, 1 however, asserts its presence in 

 the Opossum, but states that it is absent in the Koala. 



Semi-tendinosus (PI. III. fig. I, s.t., and fig. 2, s.t. ; PL IV. fig. 5, s.t, and fig. l,s.t.).— 

 In both animals this muscle has the usual origin from the tuber ischii, and in both its 

 origin is partially 1 tlended with that of the biceps proper. Its connections with the super- 

 caudal portion of the biceps have already been noticed. In Cuscus it is inserted into I he 

 inner aspect of the tibia about its middle, and completely under cover of the gracilis (PI. 

 III. fig. 2, s.t.) ; in Thylacine it is inserted very much higher up, and at a lower level than 

 the gracilis (PI. IV. fig. 1, s.t.). 



In Thylacine the muscle is traversed by a faint tendinous intersection, but no such 

 appearance was visible in Cuscus. It is a rare occurrence to find such in the semi- 

 tendinosus of a Marsupial. 



Semi-membranosus. — Little need be said about this muscle. It has the usual origin, 

 and it ends in a round tendon which passes under cover of the strong cord-like internal 

 lateral ligament (PL III. fig. 1, ill.) of the knee to be inserted into the side of the anterior 

 tuberosity of the tibia. It acts, therefore, as a rotator of the leg upon the thigh, as well 

 as a powerful flexor (PL III. fig. 2, s.m., and PL IV. fig. 1, *.///.). 



Muscles on the Anterior and Liner Aspects of the Thigh. 



Sartorius. — In both cases this muscle arises from the anterior superior spine of the ilium. 

 In Cuscus, owing to the flexed condition of the thigh, it is at first closely applied to the 

 lower part of the abdominal wall. Expanding into an exceedingly thin sheet of muscular 

 fibres, it is inserted into the tendinous expansion of the quadriceps extensor muscle on the 

 front of the knee, and also into the fascia upon the inner aspect of the joint (PL III. 

 flo-. 1, s.). In Thyl acinus it is a thick prismatic muscle, and is inserted entirely in front 

 of the knee-joint into the quadriceps expansion. 



These animals therefore prove no exception to the rule that in Marsupialia generally 

 the sartorius acts chiefly as an extensor of the leg upon the thigh. 



1 Myology of the Wombat and Tasmanian Devil, Ann. and Mag. Nat. Bist, vol. v., 4th Bar. 



2 Muscular Anatomy of Koala, Jour, of Anat, and Phys., vol. xvi. p. -1'io. 



