46 FORM AND ACTION. 



r 



called passaging or shouldering-in, mostly resides in the rotatory 

 motion possessed by this joint. 



Viewing the relative positions of the bones of the fore-limb in the 

 standing posture {see Fig. Ill), we perceive that the two composing 

 the shoulder constitute, in situ, an angle of an obtuse character, hav- 

 ing two sides ; a superior, formed by the scapula ; an inferior and 

 shorter one, by the humerus : the point of the angle being turned 

 forwards. This oblique or angular arrangement is attended with 

 several manifest advantages. A larger extent of surface upon the 

 side of the body is occupied and embraced by the bones so dis- 

 posed, thus affording more extensive and firmer attachment of the 

 limb to the trunk. At the same time that this angular apposition 

 better ensures their connexion with the ribs, it likewise affords 

 the bones facility of motion upon each other, without risk of dis- 

 severation or detachment from the sides of the chest; for the 

 movements of the shoulders, which in action are considerable, 

 have to be carried on, not only while the foot is off the ground, 

 but at a time when all the weight of the body is imposed upon 

 them. Another advantage of the angle is the extensive border- 

 ing and powerful leverage offered for the attachment and operation 

 of muscle. Had the bones of the shoulder been placed upright or 

 perpendicularly, one upon the other, in the first place, they could 

 not have been made any thing like their present length; in the 

 second, their connexion with the body would not have been equally 

 secure ; and, in the third place, their movements upon each other 

 must have been comparatively restricted, giving rise to something 

 in the form of action in the fore-limbs a great deal worse than 

 that paddling sort of going which we denominate " pinned in the 

 shoulders." This will appear more intelligible after we have shewn 

 what is the nature of the motions or action of the shoulders. 



The muscles attaching the scapulee to the sides of the chest 

 impart to the shoulders that strength which enables them to sup- 

 port the fore parts of the animal machine, and move under their 

 burthen with a facility that no joint or other contrivance could 

 have afforded them. The scapula or blade-bone, in the position 

 we behold it while the horse is standing, possesses — in relation to 

 an imaginary line let fall perpendicularly from the withers (see 

 Fig. IV, C D) — a degree of inclination or obliquity which varies 



