158 



EXTREMITY. 



cms with the posterior thick edge of the spine 

 of the scapula, and viewed from above ap- 

 pears to be merely an expansion of it. The 

 narrowest part of the process is where it seems 

 to spring from the spine, forming a sort of 

 pedicle. Its posterior surface is convex, rough, 

 covered with fibrous tissue in the recent state ; 

 its aspect is upwards and backwards. Here 

 the process is quite subcutaneous as the pos- 

 terior part of the spine of the scapula. The 

 anterior surface is concave, smooth, looks 

 downwards and forwards to the posterior and 

 superior part of the shoulder-joint. The 

 posterior or inferior edge of the process con- 

 tinuous with the corresponding edge of the 

 spine of the scapula forms a curve, convex 

 downwards and outwards, and terminates 

 in the pointed extremity or apex of the pro- 

 cess; all this edge affords attachment to the 

 deltoid muscle. The superior edge is con- 

 cave ; near the apex we observe upon it a 

 plane oval articular surface to which the acromial 

 extremity of the clavicle is articulated ; into 

 this edge the trapezius muscle is inserted. 

 The apex of the acromion, which is imme- 

 diately in front of the articular surface for the 

 clavicle, gives insertion to the apex of the liga- 

 ment, whose base is attached to the outer edge 

 of the coracoid process. 



The scapula is connected to the trunk through 

 its articulation with the clavicle, but chiefly 

 through the intervention of muscles, so that 

 muscles are inserted into all its edges, and its 

 surfaces are " cushioned with muscles." It is, 

 then, as might be anticipated, a very moveable 

 bone, and its motions consist in more or less 

 extensive revolutions round an axis through its 

 centre. This bone, then, being the medium 

 of connexion between the pectoral extremity 

 and the trunk, it is evident that the great move- 

 ments of the former must depend upon the 

 movements produced in the scapula by the 

 muscles which pass to it from the trunk; more- 

 over, when some of these muscles fix the 

 scapula, it becomes the point whence the others 

 act in producing the motions of the ribs. The 

 scapula, then, is an essential element in the 

 upper extremity, and it exists wherever we 

 find that limb in a perfectly developed state, 

 but it experiences various modifications in 

 position and shape according to the uses to 

 which the upper extremity is applied. In 

 quadrupeds the position of the scapula is more 

 forwards and on the side of the chest, for in 

 them the anterior extremity is employed as an 

 instrument of support. It is interesting to 

 observe the variation in the aspect of the glenoid 

 cavity, according to the oblique or upright 

 position of the scapula, indicating whether 

 the pectoral extremities are used chiefly as 

 instruments of support or as instruments of 

 prehension, Stc. When freedom and rapidity 

 of motion are required conjoined with strength, 

 we find the scapula placed obliquely over the 

 ribs, and a corresponding obliquity between 

 the humerus and scapula. " In the horse, as 

 in most quadrupeds, the speed results from 

 the strength of the loins and hinder extremities, 

 for it is the muscles there which propel the 



animal. But were the anterior extremities 

 joined to the trunk firmly and by bone, they 

 could not withstand the shock from the descent 

 of the whole weight thrown forwards ; even 

 though they were as powerful as the posterior 

 extremities they would suffer fracture or dis- 

 location. We cannot but admire, therefore, the 

 provision in all quadrupeds whose speed is 

 great, and whose spring is extensive, that, from 

 the structure of their bones, they have an 

 elastic resistance by which the shock of descend- 

 ing is diminished. 



" If we observe the bones of the anterior 

 extremity in the horse, we shall see that the 

 scapula is oblique to the chest, the humerus 

 oblique to the scapula, and the bones of the 

 fore-arm at an angle with the humerus. Were 

 these bones connected together in a straight 

 line, end to end, the shock of alighting would 

 be conveyed through a solid column, and the 

 bones of the foot or the joints would suffer 

 from the concussion. When the rider is thrown 

 forwards on his hands, and more certainly when 

 he is pitched on his shoulder, the collar-bone 

 is broken, because in man this bone forms a 

 link of connexion between the shoulder and 

 the trunk, so as to receive the whole shock ; 

 and the same would happen in the horse, the 

 stag, and all quadrupeds of great strength and 

 swiftness, were not the scapula sustained by 

 muscles and not by bone, and did not the 

 bones recoil and fold up." 



" The horse-jockey runs his hand down the 

 horse's neck in a knowing way and says, ' this 

 horse has got a heavy shoulder, he is a slow 

 horse.' He is right, but he does not under- 

 stand the matter; it is not possible that the 

 shoulder can be too much loaded with muscle, 

 for muscle is the source of motion and bestows 

 power. What the jockey feels and forms his 

 judgement on is the abrupt transition from the 

 neck to the shoulder, which, in a horse for the 

 turf, ought to be a smooth undulating surface. 

 This abruptness or prominence of the shoulder 

 is a consequence of the upright position of the 

 scapula ; the sloping and light shoulder results 

 from its obliquity. An upright shoulder is the 

 mark of a stumbling horse it does not revolve 

 easily to throw forward the foot."* 



A comparison between the skeleton of the 

 anterior extremity in the elephant and in one 

 of the stag kind illustrates how the oblique 

 position of the scapula is favourable to rapidity 

 of motion, while the upright position is that 

 most calculated for supporting weight. In the 

 elephant the glenoid cavity of the scapula is 

 placed vertically over the head of the humerus, 

 and all the other component parts of the limb 

 are similarly disposed, so as to form a complete 

 pillar of support for the trunk. Hence the 

 attitude of standing in the elephant requires 

 but slight muscular effort, and in this position 

 he is in such complete repose as often to obtain 

 sleep. In this animal, then, the angle between 

 the scapula and humerus is nearly obliterated, 

 but in the stag it approaches closely to a right 

 angle, the scapula is oblique to the ribs, and 



* Sir Charles Bell, Bridgcwater Treatise. 



