528 SCIENCE PROGRESS 



lies between the tongue and the larynx, and for this reason the 

 muscle is called by many anatomists the genio-hyo-glossus. 

 When the tongue is at rest the front fibres of this muscle follow 

 the outline of its under-part as seen from the front, and hence are 

 concave forwards. The central and posterior fasciculi of this 

 fan-like muscle are usually almost straight. The very fact of 

 its spreading from its point of origin like an open fan shows 

 that there is a widening interval between the composing bundles 

 of muscular tissue as they pass to their place of insertion, which 

 interval is filled up by loose connective tissue comparable to 

 that which lies between contiguous muscles elsewhere, in order 

 to allow free movement between the neighbouring parts. There 

 are two of these muscles lying side by side separated by that 

 gristly septum which divides our tongue into two almost distinct 

 halves. One marked peculiarity of the muscle in man it may 

 be as well to describe here. It gets its nerve supply from the 

 ninth pair of cerebral nerves (the hypo-glossal) and each fasciculus 

 receives a distinct branch, just as if it were a separate muscle. 



Now it is plain that whatever the functions of the genio- 

 glossus may be (and that they are very important is shown by 

 its greatly increased size in man as compared with other animals) 

 it requires considerable room beneath the tongue in which to 

 exercise those functions. If we examine it in most of the lower 

 animals we find it is merely a feeble slip of flesh lying in a 

 position too cramped to be of any great service, since in dogs, 

 cats, pigs, and most other quadrupeds the tongue lies in almost 

 immediate contact with the inner surface of the jaw. 



Now we come to some exceedingly curious and suggestive 

 facts. In the apes this muscle begins to show signs of having 

 important functions. These functions probably are to enable 

 the tongue to move freely about the mouth for the purpose of 

 sorting the food which is already there and rejecting such things 

 as nutshells which are of no use to the animal. If we examine 

 the lower jawbone of any ape we find that there is on its inner 

 side a deep pit or hole specially to accommodate the genio-glossus 

 muscle. Outwardly many of the apes, and especially the baboons, 

 bear a considerable resemblance to dogs, but no one could possibly 

 mistake the lower jawbone of a baboon for that of a dog. 



Here we have a very remarkable difference of structure 

 between ourselves and all our nearest relations in the animal 

 world. In man the genio-glossus muscle springs from the top 



