SESAMOID BONES. 



541 



not effect the metamorphosis. While Jhe 

 complete isolation of these bodies from the 

 vessels which are the immediate channels of 

 nutrition, leaves only one supposition, viz., 

 that the synovial fluid is the pabulum from 

 which they derive the materials essential to 

 their permanence, growth, or alteration. The 

 composition of this fluid as compared with 

 their own, perhaps sufficiently warrants this 

 conclusion. 



Other conjectures as to the mode of their 

 development are offered by Bidder, such us 

 the possible precipitation of synovia around 

 an epithelial cell, the gigantic development of 

 a cell, or, what much approximates to this, 

 their hydatid nature. 



In certain abnormal conditions of the ar- 

 ticular cartilages, peculiar appearances of the 

 synovial membranes are seen, although it is 

 somewhat doubtful how far they can be re- 

 garded as essentially morbid. 



Thus, for example, in the ulceration of diar- 

 throdial cartilages, it appears probable, that 

 the removal of their substance is chiefly 

 accomplished by the synovial membranes. 

 Ouveilhier * narrates a case in which puru- 

 lent fungosities of this tissue replaced the 

 destroyed cartilages of the ankle-joint; and the 

 general connection of hypertrophy of the 

 membrane with ulceration of the cartilage has 

 long been known. More recently, Mr. Ciiood- 

 sir'sf investigations have thrown much ad- 

 ditional light on this subject. He has shown 

 that the preternaturally active growth of the 

 cartilage, and the similarly rapid change of its 

 properties and appearances, are to be regarded 

 as inherent in this tissue itself; that where 

 the destruction of its substance occurs at its 

 margin, or in the immediate neighbourhood of 

 the vessels, a fungous enlargement or ex- 

 tension of these accurately fits into the eroded 

 part ; but that in the ulceration of the centre 

 of the cartilaginous lamella, such a physical 

 adaptation is absent. From these circum- 

 stances it seems probable that the absorption 

 which is accomplished in the former case by 

 the local enlargement, is in the latter shared 

 by the vessels of the synovial membrane 

 generally. 



A somewhat similar, but much less pro- 

 minent affection of vascularity has been de- 

 scribed by Dr. Todd J in the porcelain-like 

 condition of these cartilages, which often 

 obtains in the chronic gout of the aged. 

 The highly injected vessels of the synovial 

 membrane were covered by a whitish powder, 

 which was doubtless a frictional detritus of 

 the diseased cartilage. How far this con- 

 gestive state is connected with the absorption 

 of this powder, is unknown. 



(William Briuton.) 



SESAMOID BONES. By this name are 

 designated the small bones met with in the 

 neighbourhood of certain joints, generally in 

 the tendons of the adjacent muscles. They 



* Archives Ge'ue'rales de Medecine, vol. iv. p. 101. 

 t Anatomical and Pathological Observations, 

 j Medical Gazette, 1847. 



owe their name (<7?;rT//); aooe) to the figure 

 which they usually possess, resembling that 

 of an Indian grain called sesame. But the 

 present application of the term regards the 

 character of their situation in the course of 

 a tendon, rather than their form ; for in- 

 stance, the patella is often said to be a sesa- 

 moid bone, not because it resembles sesame, 

 but because it is placed in the tendon of the 

 extensor cruris muscles. This character of 

 their situation in the course of tendons con- 

 stitutes their chief point of interest; it is in 

 this that they are peculiar, and different from 

 other bones. 



In the human subject these bones are 

 usually met with only on the palmar aspect of 

 the metacarpo-phalangeal joint of the thumb 

 and the homologically corresponding part of 

 the great toe, in both of which situations there 

 are usually two. These are not constantly 

 present, and, according to Cloquet, are not met 

 with in children, owing, probably, to their 

 becoming ossified late, though in young Ru- 

 minants and Solipeds, as well as in other 

 animals, I have found their ossification as far 

 advanced as it was in the other bones. They 

 are more frequently absent in the hand than 

 in the foot, and in females than in males. The 

 long flexor tendon of the thumb or great toe 

 passes between them, and the two are bound 

 together above and below it by dense fibrous 

 tissue, so that they assist in forming its 

 sheath. 



The sesamoid bones of the thumb are very 

 small usually not bigger than the half of a 

 large pea. They have a somewhat oval out- 

 line, are convex on their palmar, and slightly 

 concave on their dorsal aspect, which is arti- 

 cular, and covered with cartilage. They arti- 

 culate with the head of the metacarpal bone. 

 Those of the great toe are each as large as a 

 horse bean, of a long oval outline, convex on 

 the plantar aspect, and presenting a concave 

 cartilage-covered surface to the head of the 

 metatarsal bone, to which they are adapted. 



The little pieces of bone, situated and 

 shaped as above, are enclosed in the tendons 

 of the short flexor muscle of the thumb or 

 great toe, the fibres of which have the follow- 

 ing relation to them : Some of the ten- 

 dinous fibres pass over them, and some on 

 each side, whilst their articular cartilage, as I 

 have verified by microscopic examination, be- 

 comes mixed with tendinous fibres, passing on 

 their arthrodial aspect, as it approaches the 

 bone. The greater part of the tendon, how- 

 ever, is inserted into their proximal, and arises 

 again, so to speak, from their distal end. The 

 arthrodial surface of their articular cartilage 

 forms part of the synovial surface of the sub- 

 jacent metacarpo-phalangeal joint, and they 

 are held in their place by the strong fibrous 

 tissue of the common synovial capsule. 



Structure. The sesamoid bones consist of 

 finely cancellated osseous tissue, enclosed in a 

 shell of denser bone. The main direction of 

 the osseous columns that surround the can- 

 celli is longitudinal, but they intercommunicate 

 in all directions. These columns are much 



