SESAMOID BONES. 215 



The sesamoid bones of the joints in the upper extremity, are two on the palmar 

 surface of the metacarpo-phalangeal joint in the thumb, developed in the tendons 

 of the Flexor brevis pollicis ; occasionally one or two opposite the metacarpo- 

 phalangeal articulations of the fore and little fingers ; and, still more rarely, one 

 opposite the same joints of the third and fourth fingers. In the lower extremity, 

 the patella, which is developed in the tendon of the Quadriceps extensor ; two small 

 sesamoid bones, found in the tendons of the Flexor brevis hallucis, opposite the 

 metatarso-phalangeal joint of the great toe ; and occasionally one in the metatarso- 

 phalangeal joint of the second toe, the little toe, and, still more rarely, the third 

 and fourth toes. 



Those found in the tendons which glide over certain bones occupy the following 

 situations : one sometimes found in the tendon of the Biceps cubiti, opposite the 

 tuberosity of the radius : one in the tendon of the Peroneus longus, where it glides 

 through the groove in the cuboid bone ; one appears late in life in the tendon of the 

 Tibialis anticus, opposite the smooth facet of the internal cuneiform bone ; one is 

 found in the tendon of the Tibialis posticus, opposite the inner side of the head of the 

 astragalus ; one in the outer head of the Gastrocnemius, behind the outer condyle 

 of the femur; and one in the conjoined tendon of the Psoas and Iliacus, where it 

 glides over the os pubis. Sesamoid bones are found occasionally in the tendon of 

 the Glutens maximus, as it passes over the great trochanter, and in the tendons 

 which wind round the inner and outer malleoli. 



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