96 



muscles, a very important clew seems to be af- 

 forded by the analogy of those muscles, which, in 

 the horse, replace the sterno-mastoids in man. 

 These are (see note to 86) one muscle, which goes 

 from either upper corner of the sternum to the rear 

 part of the lower jaw, so that its action will close 

 the jaw ; or, this done, bring down the head toward 

 the breast ; and a second, which goes from the raas- 

 toid protuberance, and the anterior C part of the 

 neck S to the upper part of the upper arm-bone, the 

 action of which is "to raise the shoulder and arm, 

 and at the same time draw them forward, or, these 

 being fixed, to turn the neck and head to one side." 



We should conclude from these facts, as an- 

 alogues, that certain effects, accompanying the 

 motions given to the sterno-mastoids by the upper 

 comers of the sternum, largely, even if indirectly, 

 affect the motions of the lower jaw ; and also that 

 the clavicle (collar bone) in man secures certain 

 connections between the motions of the head and 

 the arm-bone, and between the sternum and the 

 lower jaw, which for the horse (it having no collar 

 bone) must be supplied by extra muscles. 



It would seem that when the sterno-mastoid of 

 the left side was dratvn tight, i. e., (§ 93), when the 



