THE MUSCLES 59 



holds that it is derived from the posterior fibres of the M. inter- 

 hyoideus which have shifted their origin in a similar manner to the 

 main portion, and have also migrated backwards and obtained a 

 secondary attachment to the skin of the gular fold. 



Innervation-. From R.jugularisVII, which bends over the posterior 

 edge of the muscle at its origin and then enters it from the dorsal 

 surface. 



Function : The muscle must obviously act in more than one way. 

 In so far as it acts as a constrictor of the pharynx — the anterior fibres 

 in particular — it must be of importance in swallowing food and in 

 breathing, while, by virtue of their attachment to the skin and to the 

 fascia pectoralis^ the simultaneous contraction of the posterior fibres 

 on both sides would tend to depress the head, and the contraction of 

 one side at a time would cause the head to incline sideways. 



The three muscles just described are all superficial, and are seen 

 directly the skin is removed. In order to expose the remainder of 

 the hyobranchial muscles it is necessary to cut along the linea alba, 

 and turn back the MM. intermandibularis and interhyoidei. 



M. subhyoideus (Driiner, in Ellipsoglossa) (m.s.hy.). 



Cerato-glossi extern! ...... Funk (1827). 



Os hyoides protrahens (14) ..... Carus (1828). 



Geniohyoideus anticus et posticus . . . v. Siebold (1828). 



Genio-hyoideus lateralis ..... Druner (in Sal. 1901). 



This is the last of the Vllth nerve muscles. It arises from the 

 posterior end of the cerato-hyal^ which it encloses in a sort of muscular 

 cup. It is narrow and ribbon-like in form, and its fibres run approxi- 

 mately parallel with and ventral to the cartilage from which it arises. 

 The muscle widens a little at its insertion, which is on the dorsal side 

 of the aponeurosis of the M. intermandibularis. 



The homology of this muscle is in some doubt. Druner regarded 

 it as the anterior portion of the larval interhyoideus, and its position 

 and innervation are certainly in agreement with this view. On the 

 other hand, the work of Miss Louise Smith (1920) on the develop- 

 ment of the hyobranchial muscles of Spelerpes seem to be against 

 it. Miss Smith describes muscle which she calls 'genio-hyoideus 

 lateralis' which appears to be homologous with the muscle just 

 described. Nevertheless, in Spelerpes — according to Miss Smith — 

 it is proliferated not from the anlage of the interhyoideus but 

 from that of the genio-hyoideus. Now the M. genio-hyoideus 

 is a muscle belonging to the hypoglossal (first spinal) nerve, and 

 all muscles derived from the same anlage should be innervated 



