of the Leg of the Ostrich, 265 



inserted on the outer side of the capsule of the knee-joint. Its 

 weight is 25 J oz. Its action is to the outside of the plane that 

 coincides with the greatest diameter of the highly elliptical cross 

 section of the femur. (2) arises from the whole outer surface 

 of the femur (fig. II.) ; it has an insertion similar to that of (1). 

 Its weight is 5 oz. 



9, 10. The vastus internus, like the preceding, is composed of 

 two parts, whose origins are shown in fig. III. (1) arises from 

 the upper and inner surface of the femur, and is inserted into 

 the inner side of the head of the tibia, into the inner edge of 

 the patella and of the ligamentum patellae. Its weight is 131 oz. 

 (2) arises from the lower portion of the inner surface of the 

 femur, and is inserted into the tendon of the former, (1). Its 

 weight is 3| oz. 



The resultant plane of these two muscles lies as much to the 

 inside of the plane of maximum strength of the femur as that of 

 the vasti extcrni lies to the outer side of the same plane. 



11. M. crurseus. Its origin, which lies altogether on the 

 inner side of the femur, is shown in fig. III. It is inserted, with- 

 out a tendon, into the patella. Its weight is 7 J oz. Its plane of 

 moment coincides very nearly with that of the vasti interni just 

 described ; and it is almost impossible to avoid coming to the 

 conclusion that the peculiar elliptical cross section of the femur 

 and its longitudinal plane of maximum strength are contrived 

 with reference to the strains of these muscles, so as to enable 

 the slight and delicate structure of the femur (peculiar to all 

 birds) to resist the action of the forces brought to bear upon it, 

 and which exceed in magnitude those acting on the limbs of 

 most quadrupeds. 



12. The rectus femoris muscle is not correctly described in 

 any book that I have seen ; and its true nature and connexion 

 with the muscles of the calf were discovered by me quite acci- 

 dentally. I had taken it for granted that the rectus femoris 

 terminated in the patella; but, as there were two patellas, 

 I wished to know in which of them the muscle terminated. 

 On dissection, to my surprise I found that, instead of ending 

 in either patella, its tendon passed in a groove over and between 

 them both, and, turning outwards and backwards into the calf 

 of the leg, became provided with a second muscular belly, which 

 formed one of the portions of the flexor magnus digitorum, 

 the conjoined tendon of which passed under the heel and termi-- 

 nated in the plantar surface of the toe. 



The rectus femoris, with its tendon, is therefore truly a di- 

 gastric muscle, upwards of 5 feet in length (fig. IV.), and has its 

 origin in the anterior bony prominence of the ilium (fig. I.), 

 which is well marked on every pelvis of the Ostrich that I have 



