254 



ARTICULATION. 



pears as a consequence of paralysis, and hence 

 also the greater liability to luxation which 

 exists in a debilitated state of the system. 

 Articular or capsular muscles thus placed, have 

 also the effect, as it is said, of preventing 

 the pinching of the capsule or synovial mem- 

 brane between the articular extremities of the 

 bones in the different motions of the joint. 



The joints are very generally copiously sup- 

 plied with blood, and are remarkable for the 

 arterial anastomoses which take place around 

 them. The best examples of these are met with 

 in each of the joints of the extremities. The 

 parts supplied with blood are the synovial 

 membranes, the ligaments, the fat, and the extre- 

 mities of the bones; but the cartilages cer- 

 tainly do not receive vessels carrying red 

 blood : I believe there is no fact in anatomy, 

 more generally admitted or better determined 

 than this. The vascular ramifications which 

 proceed from these vessels may be seen, par- 

 ticularly in young subjects, advancing in the 

 subsynovial cellular tissue, and forming a vas- 

 cular net-work there, as far as the margin of the 

 articular cartilage where they stop abruptly ; 

 this is what W. Hunter described under the 

 name of circulus articuli vasculosus. 



Of the forms and classification of the arti- 

 culations. It is not difficult, by passing in 

 review the various motions which take place 

 between any two segments of a limb, to form 

 an idea, a priori, as to the kinds and shapes 

 of the articulations by which these segments 

 will be united ; it is only necessary not to lose 

 sight of the fact, that in the construction of a 

 joint regard is had not to its mobility alone, 

 but to its security, its durability, and the safety 

 of the neighbouring parts. VVe may expect 

 to find joints varying in the degree of motion, 

 from the slightest perceptible quantity, to the 

 freest that is compatible with the maintenance 

 of the segments in their proper relation with 

 each other, and also in extent of motion, from 

 that which is so slight as to admit of almost 

 no appreciable change in the position of the 

 parts, to that which allows of the most ample 

 variety of relation between the segments, 

 consistent with the integrity of the articula- 

 tion. 



It will appear, then, that the most simple 

 kind of articulation is that by which two parts 

 are so united as that the slightest appreciable 

 degree of motion only shall exist between them. 

 This constitutes the first great division of joints 

 the Synarthrosis (crvv, cum, and agOgov, arti- 

 culus) where the parts are continuous, i. e. 

 not separated from each other by an intervening 

 synovial cavity. Some anatomists consider all 

 synarthrodial joints to be immoveable; which, 

 although not ifar from the truth, cannot be said 

 to be strictly accurate. Had immobility been 

 the object to be obtained, I imagine that that 

 might have been more effectually accomplished 

 by the fusion of the extremities of the segments 

 together, as in anchylosis. 



In the second class of joints, motion is 

 enjoyed freely and fully: this class is designated 

 by the term Diarthrosis (&*, per, and a 



the segments are interrupted completely in 

 their continuity ; the extremities of the bones 

 can only be said to be contiguous. 



Synarthrosi*. The general characters of the 

 articulations belonging to this class are, 1. 

 that they are very limited in their motion, 

 insomuch as to be considered by some as im- 

 moveable ; 2. that their surfaces are continuous, 

 i. e. without the intervention of a synovial 

 cavity, but with that of some structure different 

 from bone. The following varieties may be 

 noticed among synarthrodial articulations. 



a. Suture (Germ. Natli or Naftt. Com- 

 missura cranii, Vesal.). When the margins of 

 two bones exhibit a series of processes and 

 indentations (dovetailing) which are received 

 and receive reciprocally, with a very thin car- 

 tilaginous lamina interposed, this is the ordi- 

 nary kind of suture, sutura vera, of which 

 three kinds are distinguished : sutura dcntata, 

 where the processes are long and dentiform, as 

 in the interparietal suture of the human skull; 

 sutura serrata, when the indentations and 

 processes are small and fine like the teeth 

 of a saw, as in the suture between the two por- 

 tions of the frontal bone ; sutura limbosa, when 

 there is along with the dentated margins a 

 degree of bevelling of one, so that one bone 

 rests on the other, as in the occipito-parietal 

 suture. 



When two bones are in juxta-position by 

 plane but rough surfaces, the articulation is 

 likewise said to be by suture, and this is the 

 false suture, sutura notha, of which there are 

 two kinds : sutura squamosa, where the be- 

 velled edge of one bone overlaps and rests 

 upon the other, as in the temporo-parietal 

 suture, and harmonia (*;, adapto), where 

 there is simple apposition : this last kind of 

 articulation is met with, as Bichat* observes, 

 wherever the mechanism of the parts is alone 

 sufficient to maintain them in their proper 

 situation, as may be seen in the union of most 

 of the bones of the face. 



It is in the .articulation of the bones of the 

 skull and face of animals, as has been already 

 noticed, that we see the best examples of su- 

 tures. In the chelonian reptiles, as the tortoise, 

 the bodies, laminae, and spinous processes of the 

 vertebrae are united by suture, and the same 

 mode of articulation unites the elements of 

 the sternum of the land-tortoise to each other.f 

 The bones of the head of birds and fishes 

 are united chiefly by the harmonic and squamous 

 sutures. In the lateral parts of the heads of 

 fishes, and in the opercula of their gills, as 

 between the opercular and subopercular bones, 

 there is a species of articulation, most re- 

 sembling the squamous suture, but differing 

 from it in admitting a considerable latitude of 

 motion by which these bones can glide on 

 one another 4 To descend still lower in the 

 scale, we may observe a mode of joining very 

 similar to suture, between the tubercular and 



* Anat. Gen. t. iii. p. 63. 



t See Grant's Comp. Anat. p. 83, fig. 43. 



t Cuvier, Lecons d'Anat. Comp t.. i. p. 125. 



