258 SPECIAL ANATOMY OF THE SKELETON 



the parts over which they glide. It is said that they are more commonly found in 

 the male than in the female, and in persons of an active muscular habit than in 

 those who are weak and debilitated. They are invested throughout their whole 

 surface by the fibrous tissue of the tendon in which they are found, excepting upon 

 that side which lies in contact with the part over which they play, where they 

 present a free articular facet. They may be divided into two kinds those 

 which glide over the articular surfaces of the joints, and those which play over 

 the cartilaginous facets found on the surfaces of certain bones. 



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

 surface of the metacarpophalangeal joint in the thumb, developed in the tendons 

 of the Flexor brevis pollicis; one on the palmar surface of the interphalangeal 

 joint of the thumb; occasionally one or two opposite the metacarpophalangeal 

 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; one sometimes over the interphalangeal joint 

 of the great toe; and occasionally one in the metatarsophalangeal 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 brachii, 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 around the inner and outer malleoli. 



