THE SHOULDER. 359 



Wo comuieuce with the upper portion, of Avhich the fore cxtremitj-, the 

 shoulder, is seen at G, page 140. 



THE SHOULDER. 



The scapula or shoulder-blade, situated forward on the side of the chest, 

 is a bone of a somewhat triangular shape, with its apex or narrowest point 

 dowmvard, and its broad and thin expansion upward. The point of the 

 shoulder hes opposite to the first and second ribs ; the hinder expansion of 

 the base reaches as far back as the seventh rib ; it therefore extends 

 obliquely along the chest. It is divided, externally, into two unequal 

 portions by a ridge or spine running through almost the whole of its extent, 

 and desig-ned, as will be presently seen, for the attachment of important 

 muscles. The broad or upper part, having no muscles of any consequence 

 attached to it, is terminated by cartilage. 



The shoulder-blade is united to the chest by muscle alone. There is one 

 large muscle, with very remai-kable tendinous fibres and of immense strength 

 (the serratus viagnus, great saw-shaped muscle), attached to the chest, 

 all the true ribs, and to the upper third of the internal sui-face of the 

 shoulder-blade, and the four last cervical vertebra?, and by which, assisted, 

 or rather strengthened, by the other muscles, the weight of the body is 

 supported, and the shock of the -widest leap, or the most rapid motion, 

 sustained. Had there been a bony union between the shoulder and the 

 body, the vital parts contained in the chest could not have endured the 

 dreadfnl shock which they would occasionally have experienced ; nor 

 could any bone have long remained Avhole if exposed to such violence. 

 The muscles within the shoulder-blade act as powerful and safe springs. 

 They yield, as far as necessary, to the force impressed upon them. By 

 their gradual yielding they destroy the violence of the shock, and then by 

 their elastic power, imniecliately gain their former situation. 



SLANTING DIRECTION OF THE SHOULDER. 



The lessening or breaking of the shock, from the vfeight being thrown 

 violently on the fore legs, is effected in another way. It -will be obsei-ved, 

 that (see Gr and J, p. 140) the shoulder-blade and the lower bone of the 

 shoulder are not connected together in a straight line, but form a very 

 considerable angle with each other. This wall be more e\ddent from the 

 foUowdng cut, which represents the fore and hind extremities in the situa- 

 tions which they occupy in the horse. 



This angular construction of the limbs reminds us of a similar arrano-e- 

 ment of the springs of a carriage, and the ease of motion, and almost per- 

 fect freedom from jolting, which are thereby obtained. 



It must not perhaps be said, that the form of the spring was borrowed 

 from this construction of the Hmbs of the horse, but the efiect of the 

 carriage- spring beautifully illustrates the connection of the different bones 

 in the extremities of this quadruped. 



The obliquity or slanting direction of the shoulder effects other very 

 useful pui'poses. That the sti^ide in the gallop, or the space passed over 

 in the trot, may be extensive, it is necessary that the fore part of the animal 

 should be considerably elevated. The shoulder, by means of the muscles 

 which extend from it to the inferior part of the limb, is the grand agent 

 in effecting this. Had the bones of the shoulder been placed more 

 upright than we see them, they could not then have been of the length 

 which they now are — their connection w4th the chest could not have 

 been so secure — and theu" movements upon each other w^ould have been 



