SESAMOID BONES. 129 



other toes with the first and third phalanges ; and the third, with the se- 

 cond row. 



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

 toe, the innermost tendon of the extensor brevis digitorum, abductor pol- 

 licis, adductor pollicis, flexor brevis pollicis, and transversus pedis ; second 

 toe, first dorsal and first palmar interosseous and lumbricalis ; third toe, 

 second dorsal and second palmar interosseous and lumbricalis ; fourth toe, 

 third dorsal and third palmar interosseous and lumbricalis ; fifth toe, 

 fourth dorsal interosseous, abductor minimi digiti, flexor brevis minimi 

 digiti and lumbricalis. Second phalanges ; great toe, extensor longus pol- 

 licis, and flexor longus pollicis ; other toes, one slip of the common tendon 

 of the extensor longus and extensor brevis digitorum, and flexor brevis 

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

 extensor longus and extensor brevis digitorum, and the flexor longus digi- 

 torum. 



SESAMOID BONES. These are small osseous masses, developed in those 

 tendons which exert a certain degree of force upon the surface over which 

 they glide, or where, by continued pressure and friction, the tendon would 

 become a source of irritation to neighbouring parts, as to joints. The 

 best example of a sesamoid bone is the patella, developed in the common 

 tendon of the quadriceps extensor, and resting upon the front of the knee- 

 joint. Besides the patella, there are four pairs of sesamoid bones included 

 in the number of pieces which compose the skeleton, two upon the meta- 

 carpo-phalangeal articulation of each thumb, and existing in the tendons 

 of insertion of the flexor brevis pollicis, and two upon the corresponding 

 joint in the foot, in the tendons of the muscles inserted into the base o? 

 the first phalanx. In addition to these, there is often a sesamoid 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 gastrocnemius. 



The bones of the tympanum, as they belong to the apparatus of hearing, 

 will be described with the anatomy of the ear. 



CHAPTER III. 



ON THE LIGAMENTS. 



THE bones are variously connected with each other in the construction 

 of the skeleton, and the connexion between any two bones constitutes a 

 joint or articulation. If the joint be immovable, the surfaces of the bonos 

 are applied in direct contact ; but if motion be intended, the opposing 

 surfaces are expanded, and coated by an elastic substance, named carti- 

 lage ; a fluiu secreted by a membrane closed on all sides lubricates their 



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