VESTIGIAL ORGANS 





to cut the gums are, strictly speaking, vestigial organs, for 

 under such conditions they are absolutely useless. 



Not only is man the possessor of numerous vestigial 

 organs in his adulc state, but he also exhibits organs of this 

 kind in his early stages of growth. Just within each nostril 

 of the human embryo, or even of the new-born babe, is a 

 small pore on the median wall of the nasal chamber (Fig. 8) . 

 This pore leads into a short, blind tube 

 in the nasal wall. The pore and tube 

 occupy exactly the position of Jacob- 

 son's organ of the lower vertebrates. 

 This organ is an accessory organ of smell, 

 which is well developed in many mam- 

 mals and other vertebrates. In verte- 

 brates other than man Jacobson's organ 

 is provided with branches from the olfac- 

 tory nerve, the nerve of smell, but in man 

 this innervation is said to be lacking. As 

 the organ disappears in man with the 

 passing of childhood, and as it never 

 shows signs of functional activity, it may 

 be recorded as a vestigial organ of 

 embryonic and early post-natal life. 



Another vestigial feature, prenatal in 

 time of occurrence, is seen in the lanugo 

 of the human embryo, the covering of fine woolly hair 

 found on the skin of the unborn human infant. This hairy 

 covering is ordinarily shed before birth, and the sepa- 

 rate hairs may often be identified in the amniotic liquor in 

 which the embryo is immersed. This hairy covering is 

 like that of the foetus of most mammals. At no time 

 can it be of functional importance to the human embryo, 



[45] 



Fig. 8. — Side 

 view of the face of 

 a human embryo, 

 showing the pore P 

 of the vestigial or- 

 gan of Jacobson at 

 the entrance to the 

 nasal cavity. After 

 His. 



