154 



EXTREMITY. 



in the lowest classes, particularly the insects 

 and zoophyta, where the nourishment of various 

 textures, and formation of secretions and excre- 

 tions, has been thought to be merely in the way 

 of imbibition from a central cavity." But it is to 

 be observed, that in several of these tribes, in 

 insects, and even in the infusory animals, recent 

 observations have disclosed a much more com- 

 plex apparatus for the movement of the fluids, 

 than was previously suspected. And, in regard 

 to the lowest zoophyta, it may be said in general, 

 that if there is little apparent provision for the 

 elaboration of the fluids, there is also little 

 occasion for it, -first, because there is little 

 variety of textures to be nourished, and 

 secondly, because the simplicity of their 

 structure is such, that all the particles of their 

 nourishing fluid, admitted into a central 

 cavity, flowing thence towards their surface, and 

 acted on by the air at all parts of that surface, 

 are similarly situate in regard to all the agents 

 by which they can be affected, and must be 

 equally fitted for the changes which the vital 

 affinities there acting on them can produce, so 

 that the same necessity for gradual intermixture, 

 and repeated agitation, of heterogeneous mate- 

 rials, does not probably exist in them, as in 

 the animals of more complex structure. The 

 analogy of their economy, therefore, is not a 

 serious objection to the inference we have 

 drawn from so many other facts, as to the 

 numerous changes which are wrought in the 

 blood of the higher animals, while circulating 

 in the vessels, and as to the function of excre- 

 tion being a necessary accompaniment of the 

 assimilation of aliment, and nutrition of tex- 

 tures, even independently of their renovation by 

 processes of ultimate deposition and absorption . 

 ( W. P. Alison.) 



EXTREMITY, (in human anatomy), mem- 

 brum, artus; Gr. ^teAos, xvhot ; Fr. extremit'e, 

 membre ; Germ. Gliedmusscn ; Ital. membra. 

 This term is used to denote certain appendages 

 most manifest in the vertebrated classes of 

 animals, employed as instruments of prehen- 

 sion, or support, or motion, also occasionally 

 employed for other purposes sufficiently in- 

 dicated by the habits of the animal. In fa- 

 miliar language we apply the word, limb, 

 synonymously, and the superior and inferior 

 limbs of man, or the anterior and posterior ones 

 of the Mammiferous Quadrupeds, are the best 

 examples by which we can illustrate our de- 

 finition. When these appendages exist in their 

 complete number, i. e. four, they are distin- 

 guished either by the appellatives already 

 mentioned, anterior and posterior, or superior 

 and inferior, or more precisely pectoral, and 

 pelvic or ventral, or again utlantal and sacral. 



In Fishes we find that in most instances the 

 anterior limbs (pectoral fins) are larger than the 

 posterior (ventral fins) : and sometimes the 

 posterior are absent altogether, as in the com- 

 mon eel. In Fishes we look for the simplest 

 form of the skeleton of the more highly de- 

 veloped limbs in Man and Mammalia: and 



* Cuvier, Lcjons, &c. 27. 



here we find, more or less obviously in dtfler- 

 ent instances, the same elements which sub- 

 sequently appear in a more distinct and com- 

 plete form. Thus, in the case of the Lophius 

 piscatorius, we find very distinctly the scapula 

 and clavicle forming the bond of connection 

 of the other bones of the limb to the trunk. 

 We can also recognize the radius and ulna, 

 what seems to be a very rudimentary humerus, 

 and the bones of the carpus, as well as the 

 phalanges, which generally greatly exceed in 

 number any arrangement that is to be found 

 in the higher classes. The ventral fins, how- 

 ever, the analogues of the posterior extremities, 

 are not so developed : while bones analogous to 

 the phalanges of the feet are found in it, we meet 

 no trace of the femur, tibia, or fibula. 



In all the other Vertebrata we find the an- 

 terior and posterior extremities developed on 

 a plan similar to that in man, with such vari- 

 ations as the manner of life of the animal 

 requires. We must, however, notice an excep- 

 tion in the case of serpents and Cetacea. In 

 the former there are no limbs, or at least the 

 merest trace of them ; in the latter the pos- 

 terior are absent, although the anterior exhibit 

 very perfectly all the elements of the human 

 upper extremity. 



We propose to devote the present article to 

 the detail of the descriptive anatomy of the 

 osseous system of the extremities in Man, 

 in whom, by reason of his erect attitude, the 

 terms superior and inferior are substituted for 

 anterior and posterior, as applied to the ex- 

 tremities of the lower animals. 



Superior extremity. The superior extremity 

 is connected to the trunk through the medium 

 of two bones, which, as being intimately con- 

 nected with the motions of the limb, first de- 

 mand attention. These bones are the clavicle 

 and scapula, and are commonly called the 

 bones of the shoulder. 



Clavicle (from claw, a key;) collar-bone ; 

 syn. ligula, jugulum, osjurcalc; Germ. Sclilus- 

 selbein. This bone is situated at the upper 

 and anterior part of the thorax, and forms the 

 anterior part of the shoulder: its direction is 

 from within outwards, so that its external end, 

 which is articulated with the scapula, is pos- 

 terior, and on a plane superior to its internal 

 end, which is articulated with the sternum. 

 It thus constitutes the key to the bony arch 

 formed at the shoulder, and hence its integrity 

 is especially necessary to the integrity of the 

 motions of the shoulder. 



The clavicle is a long bone, cylindrical, and 

 so curved as to resemble the italic J' placed 

 horizonlally. Its internal extremity is thick 

 and rounded, while its external one is flat- 

 tened; of its two curves one is internal, with 

 its convexity directed forwards ; the other ex- 

 ternal, with its convexity directed backwards. 



The internal extremity, also called sternal, 

 is formed by a gradual expansion of the shaft 

 of the bone, which, however, still preserves 

 the general cylindrical form, but is flattened a 

 little on its superior surface : in size this ex- 

 ceeds all other parts of the bone. The inner 

 surface of this extremity of the clavicle is 



