SESAMOID BONES. 99 



Attachment of Muscles. To twenty-three; to the first phalanges; 

 great toe, the innermost tendon of the extensor brevis digitorum, ab- 

 ductor pollicis, adductor pollicis, flexor brevis pollicis, and transver- 

 sus pedis ; second toe, first dorsal and first palmar interosseous and 

 lumbricalis ; third toe, second dorsal and second palmar interosseous 

 and lumbricalis; fourth toe, thirel dorsal and third palmar interos- 

 seous and lumbricalis ; -fifth toe, fourth dorsal interosseous, abductor 

 minimi digiti, flexor brevis minimi digiti, and lumbricalis. Second 

 phalanges ; great toe, extensor longus pollicis, and flexor longus pol- 

 licis ; other toes, one slip of the common tendon of the extensor lon- 

 gus digitorum, and extensor brevis digitorum, and flexor brevis digi- 

 torum. Third phalanges ; two slips of the common tendon of the 

 extensor longus and extensor brevis digitorum, and the flexor longus 

 digitorum. 



SESAMOID BONES. These are small osseous masses, developed in 

 those tendons which exert a certain degree of force upon the sur- 

 face over which they glide, or where, by continued pressure and 

 friction, the tendon would become a source of irritation to neigh- 

 bouring parts, as to joints. The best example of a sesamoid bone is 

 the patella, developed in the common tendon of the quadriceps ex- 

 tensor, and resting upon the front of the knee-joint. Besides the pa- 

 tella, there are four pairs of sesamoid bones included in the number 

 of pieces which compose the skeleton, two upon the metacarpo- 

 phalangeal articulation of each Ihumb, and existing in the tendons of 

 insertion of the flexor brevis pollicis, and two upon the correspond- 

 ing joint in the foot, in the tendons of the muscles inserted into the 

 base of the first phalanx. In addition to these there is often a sesa- 

 moid bone upon the metacarpo-phalangeal joint of the little finger, 

 and upon the corresponding joint in the foot, in the tendons inserted 

 into the base of the first phalanx ; there is one also in the tendon of 

 the peroneus longus muscle, where it glides through the groove in 

 the cuboid bone ; sometimes in the tendons, as they wind around the 

 inner and outer malleolus ; in the psoas and iliacus, where they glide 

 over the body of the os pubis; and in the external head of the gas- 

 trocnemius. 



The bones of the tympanum, belonging to the apparatus of hear- 

 ing, will be described with the anatomy of the ear. 





