Mackintosh — Muscular A/ialoin// of Chokepus didadyhis. 75 



absent as is tensor vaginss femoris, but iliocapsularis is present as a 

 small muscle, extending from the anterior inferior spine of the ilium 

 to the capsule of the joint. I^one of these muscles are alluded to by 

 Professor Humphry. 



Biceps femoris agrees with what appears to be its general condition 

 among Edentata, in consisting of two parts, one, representing the nor- 

 mal muscle, arising from the tuber ischii and inserted into the head of 

 the fibula, and upper third of the tibia, the other taking origin from 

 the whole length of the femur, and inserted into the second and third 

 fourths of thelnner edge of the tibia. Professor Humphry found some 

 fibres running fi'om the latter portion to join semitendinosus and 

 gracilis, while the rest of it formed a sheath for the calf of the leg, and 

 was inserted into the edges of the two bones of the fore leg, a condition 

 which approaches very closely to that obtaining in our specimen, as is 

 shown in Plate 4,"* which represents more particularly the relations 

 of biceps to the double insertion of gracilis ; the panniele is also well 

 seen running in behind the origin of iliacus. 



Bicipti accessorius is absent. 



Semimembranosus is large, running from the whole internal border of 

 the tuber ischii to be inserted into the tibia, above the attachment of 

 semitendinosus, which has no inscription (as was also the case in Pro- 

 fessor Humphry's specimen), arises along with the ischial portion of 

 biceps, and is inserted along with the inner half of gracilis, which con- 

 sists of two parts arising in common from the symphysis pubis ; the 

 external portion is inserted into the internal aspect of the tibia ; the 

 second joins the ischial biceps, and is inserted into the fibula and fibular 

 fascia, connected also with semitendinosus. In Arctopithecus this 

 muscle is single, but the insertion embraces all the parts described 

 above ; in the specimen of Bradypus, dissected by Dr. lEacalister, it 

 was also single, but the insertion was only into the tibial condyle, 

 whilst in the Ai, examined by Professor Humphry, the main details 

 corresponded to the arrangement in Unau. A considerable degree of 

 coalescence obtains in quadiiceps extensor cruris rectus, being but 

 slightly separable from the two vasti and crur^us, which are completely 

 fused. 



Popliteus is normal with a large fabella in its tendon of origin, 

 with which in Professor Humphry's specimen soleus is connected by 

 a thin muscular slip, the rest of the muscle arising from the upper part 

 of the fibula; we could not find any trace of the former head, and the 

 latter extended over the whole fibula ; the insertion in both was into 

 the calcaneum. 



Gastrocnemius externus arises rather higher up than usual, has no 

 fabella, and is inserted by two (?) tendons into the calcaneum ; its ten- 

 don is crossed by that of gastrocnemius inter nus at the lowest point of 



* Which is a camera lucida copy of Professor Macalister's ad haturam sketch. 

 Similai- arrangements exist in Arctopithecus, Bradypus, Manis, Cyclothurus, Myrnie- 

 cophaga, Tamandua. 



