SiGERSOx — Oil Dextral Pre-eminence. 43 



Sirenia, where there is merely a wider space between the roots of the 

 off-coming arteries, the arrangement of which remains essentially the 

 same. JS'oW; who will contend that these animals exhibit dextral 

 predominance ? Did it exist, it could not have escaped notice, more 

 especially in the yast aquatic mammals, where, if anywhere, it should 

 show itself on a large scale, where lob-sidedness would be so obvious 

 to the observer, and so inconvenient to the sea-swimming creature.^" 



Take the question in another way, and test it by the structure of 

 the animals in which authors assert dextral predominance to have been 

 observed. Aristotle, and subsequently Pliny, assigned it to the lion 

 and camel ; the writer in the Encyclopasdia to some dogs and horses ; 

 Dr. Ogle to monkeys and parrots. jN^ow, in the lion both right and 

 left common carotids come off equally fi-om a common brachio-cephalic 

 trunk, and therefore are beyond impeachment. Essentially similar is the 

 disposition of the arteries in the horse. With respect to the monkeys, 

 a few words of explanation are required. In the Chimpanzee the vas- 

 cular arrangement has been noted as similar to that in man ; but when 

 monkeys are mentioned it is not this rather rare animal which is meant, 

 but others of the group — those of the genus Inuus, including the 

 Macaques, which are more commonly seen, and in which right and left 

 carotids arise from a common brachio-cephalic trunk. Hence, if the 

 statements made as regards the presence of dextral predominance in 

 these animals be correct, this very remarkable conclusion is educed, 

 namely : that dextral predominance exists in them, not on account of 

 structure, but in spite of structure. The disposition of the arteries 

 is such as to secure a fair and equal division of the blood-supply to 

 the head, and yet they are represented as right-handed — if so, this 

 must be by acquisition merely. But it is quite possible that the 

 alleged facts were insufficiently, and therefore inaccurately, observed. 

 Contradictions have been oifered as regards both dogs and monkeys, 

 and with these contradictions my own investigations coincide.^'' In 

 every case it would require the most scrupulous vigilance to eliminate 

 from such a test the iniluence which right-handed men may have had 

 upon animals apt to imitate, and probably taught (more or less con- 

 sciously) by their human attendant or proprietor. 



The introduction of birds, as affording (in the parrot) an illustration 

 of dextral pre-eminence, owing to stnicture, would have been avoided 

 by a little reflection. The parrot has been the subject of training, and 

 is very imitative : it uses not only both feet, but also the beak as a third 



1^ The Rev. Dr. Haughton has noted the case of unequal lateral development 

 in a seal in the Dublin Zoological Gardens, in consequence of which it s\ram in a 

 circle. 



^'' The Sphinx baboon in the London Zoological has been seen to fling pro- 

 jectiles with both hands. The Aye-aye, according to Mr. Bartlett, used only the 

 left hand in feeding (Duncan — "Apes and Monkeys" — CasseWs Natural, History, 

 vol. i.) : yet, in this animal, both carotids arise from a common branch of the 

 brachio-cephalic. 



