66 THE SALAMANDER 



Innervation : The hypoglossal nerve traverses the muscle on its way 

 to the tongue, and, in doing so, supplies it with numerous fine twigs. 



Function: The muscle may act in several different ways. It may 

 depress the lower jaw, or the whole head, or it may pull forwards the 

 OS triangulare with its attached truncus arteriosus and heart according 

 to which other muscles are acting in conjunction, or in opposition. 



M. genio-hyoideus tertius (Druner). 



Driiner (1901), p. c^'t^'}^^ describes what he calls an abnormality of 

 the M. genio-hyoideus, in which a few of the most lateral fibres of 

 the muscle on the right side, instead of passing from the jaw to the 

 OS triangulares pass from the jaw to the posterior end of the cerato- 

 branchial i, and lateral to the M. subarcualis rectus i (ceratohyoideus 

 internus of Druner), which in this case was weaker than the corre- 

 sponding muscle on the left. He illustrates the muscle in Fig. 24 and 

 there labels it geniohyoideus tertius. The innervation is by fine fibres 

 from the hypoglossal nerve. 



Another case very similar to Driiner's has been observed in which 

 a muscle, apparently rather smaller than Driiner's, passed from the 

 posterior cornu of the hyoid to the anterior part of the lower jaw. It 

 was also innervated from the N. hypoglossus. 



It is interesting in this connexion to refer to the discussion given 

 on p. 59 regarding the homology of the M. subhyoideus, since it 

 seems not unreasonable to suggest that the abnormal muscle just 

 described may represent the muscle occurring normally in Spelerpes, 

 and described by Miss Louise Smith as the M. genio-hyoideus 

 lateralis. 



M. genio-glossus (m.g.gl.) Siebold (1828); Fischer (1843); Mivart 

 (1869); Druner (1901). 



Genio-hyoidei . . , . . . . Funk (1827). 



A fairly strong and somewhat extensive muscle in the Salamander, 

 having a fleshy origin from the mandibular symphysis. After re- 

 moving the M. intermandibularis the genio-glossus muscle may be 

 seen as two triangular blocks filling the angle of the 'chin', but it is 

 necessary to remove both the M. genio-hyoideus and the cerato-hyal 

 cartilages before the whole muscle is revealed. It is then seen to 

 consist of two portions : (i) a mesial portion — which is the genio- 

 glossus in the true sense — consisting of more or less parallel fibres 

 passing on either side of the middle line to become inserted in the 

 root of the tongue and in a tough ligament connecting the tongue 

 with the copula — the aponeurosis lingualis (Druner) — and with the 



