88 



If the muscles were united along the middle plane as described, or if 

 they were parallel by their opposed surfaces, then, no doubt, they would 

 simply reinforce one another ; and, considering the direction in which 

 their force is applied, it would be difficult to conceive how, under these 

 circumstances, they could serve as reciprocal antagonists, as is the case 

 with all other duplicate muscles disposed at opposite sides of the median 

 line. 



But anatomy shows that they are not parallel ; they are disposed at 

 a very acute angle, salient forwards, and are separated behind by a mass 

 of soft adipose tissue as already described. 



The triangular interval between the muscles, as likewise the adipose 

 substance which occupies it, will be readily perceived on making a 

 horizontal section of the boiled tongue of the sheep, or other mammal, 

 near its inferior surface, and through its entire length. 



Pathology shows no less conclusively a marked difference as between 

 the isolated and combined action of the Genio-hyo-glossi muscles, and 

 the existence of a very decided antagonism between them. 



In complete hemiplegia involving the face and tongue, the features, 

 as is well known, are drawn towards the unaffected side, whilst the 

 tongue in protrusion deviates to the side of paralysis ; this shows, as 

 regards the tongue, an antagonism between its protrusor muscles, but 

 of a very peculiar and exceptional character, and at the same time seems 

 to be in contravention of the law, that muscles, when paralyzed, are 

 overpowered by their antagonists, and drawn in the direction of the 

 fixed attachments of the latter. In protrusion of the tongue the muscles 

 engaged are mutually co-operative, and corrective of one another; they 

 act upon the tongue as upon a rigid lever, but acting at an angle, each 

 tends to carry it forwards and to the opposite side ; acting, however, 

 simultaneously, and with equal force, they correct one another, and 

 carry the tongue directly forwards, that is to say, in a line intermediate 

 between their respective axes (see diagram No. 2). 



In the event of one of these two forces being suspended, as occurs in 

 hemiplegia, the opposing force being now the sole agent in protrusion, 

 and free to act without correction, will carry the tongue forwards and 

 to the opposite or paralyzed side, that is to say, in the axis of its own 

 proper motion (see diagram No. 3). 



In case of partial paralysis of one of the opposing muscles, the tongue, 

 being in some degree governed by the weaker force, will advance in a 

 direction less decidedly lateral, or at an angle with the common axis of 

 motion of the two muscles, determined by their relative contractile 

 force, and directly as the difference in force between them (see diagram 

 No. 3). 



Granted that the genio-hyo-glossi muscles are the sole protrusors of 

 the tongue ; I submit — 



1st. That their action is peculiar in this; that whilst in the first 

 stage of protrusion they act, like other muscles, by traction; in the latter 

 stages they act by propulsion. 



2nd. That in propelling the tongue forwards they act upon it as a 



