TEANSACTIONS OF SECTION D. 691 



that of the various shapes of alveolar arch the elliptical is most commonly met with 

 amongst inferior, the parabolic amongst superior races ; and the former appears to 

 us to afford a far more roomy incisive region than the lattei". Callender, in a paper 

 on the ' So-called Serpent Teeth,' has shown how the contraction of the incisive 

 region may occur by arrested growth of the incisive process of the superior maxilla. 

 "We suggest that the diminished necessity for the incisors when food is eaten after 

 having been cooked carefully may account for this suppression. 



(iv.) Siqyjyression of the tico 2yresent lateralincisors is takinfj place. — Cope pre- 

 dicts that in the future civilised man's dentition will be — 



In^ Cl P| jMf, or 

 Ini C| P§ M|, 



and this view is shared by other authorities quoted above. 



Our series iv.-viii. inclusive bear out this theory very strikingly. In iv. there 

 are cases in which three well- and one ill-formed incisors are present. In v. two 

 well- and two ill-formed coexist. In vi. one tooth has disappeared. In vii. one is 

 missing, a second malformed, and finally, in viii., two are missing. It will be 

 noticed that of twenty-three cases in these series two only affect the median incisors. 

 Three of the cases are interesting as forming a family group : the eldest, F., set. 22, 

 has only the two medians ; the second, F., aet. 20, has lost the right lateral ; and 

 the third, I., ret. 17, like the eldest, has no laterals. 



(v.) The conical teeth frequently observed are a reversion to the pi-imitive type of 

 tooth. — It is interesting to note that in the cases of reversion to the archetype or 

 of gradual suppression, a tooth unable to reach full development may remain of the 

 conical form characteristic of lower dentitions than the human. This reversion is 

 not peculiar to man, as we have a skull of a Midas Rosalia in which an additional 

 premolar of a conical shape exists on one side. 



To sum up, our conclusions are as follows: — 



1. Man's original dentition included six incisors. 



2. Man's lost incisor is the lateral or lUg. 



8. The loss of these incisors is due to the contraction of the incisive region of 

 the alveolar arch. 



4. Suppression of the two present lateral incisors, in the upper jaw at least, is 

 at present taking place. 



5. The conical teeth, supernumerary ("VVedl, ' Dutten-oder Zapfenzahne '), fre- 

 quently observed, may be looked upon as a reversion to the primitive type of tooth. 



On the Nervous System of Myxine and Petromyzon. 

 By Professor D'Arcy Thompson. 



3. On the Vestigial Slrtidures of the Beprodiidive Apparatus in the Male 

 of the Green Lizard.^ By Professor Howes, F.L.S. 



The author describes in detail a specimen in which the two oviducts were fully 

 developed. He demonstrates for the species a series of stages in the development 

 of the same identical with those recorded for the male toads and frogs by Van 

 "Wittich, Marshall, and others. He claims that the constant tendency towards the 

 fuller development of the oviducts on the part of the male — so prevalent among 

 the higher vertebrata — points not towards an ancestrally hermaphroditic condition, 

 but rather towards one most nearly represented in the adult males of the living 

 Ganoids and Dipnoi. 



4. 071 the Development of the Shull in Cetacea. 

 By Professor D'Aect Thompson. 



' Published in the Jovrnal of Anatomy and Physiology, Jan. 1887. 



T Y 2 



