KTTNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 58. N:0 2. 25 



mal size. It has already dtiring lifetime had the greater part of its crown broken, or worn 

 off, but it clings to the jaw bone by means of two roots. The supernumerary molar of the 

 lower jaw is m^ of the left side, situated in a continuous series with the other molars (PI. 

 VI j fig. 3). Its crown is nearly square measuring 9 mm. in length by 8,8 in breadth, 

 and has four cusps, the anterior pair of which is somewhat greater and connected 

 by a ridge. 



The skull n:o 178 has a well developed m^ on either side of thelower jaw (PI. VI, 

 fig. 2). These are, however, smaller than the ordinary molars, measuring 7,2x6,7 mm. 

 They have only three cusps each, and these are on the' right m^ subequal, but on the left 

 the outer of the anterior pair is dominating, and much larger than the others. As these 

 supernumerary molars are somewhat worn, especially the large cusp on the left side, 

 it is evident that they have been in use working against m" when the lower jaw moved. 



Selenka has in a very interesting paper »Die Rassen und der Zahnwechsel des 

 Orang Utan»^ recorded many important facts also concerning supernumerary molars 

 which he has found in 20 % of 194 adult skulls of Orangs. Some of his statements appear 

 to refer to these Chimpanzees as well, viz. that supernumerary molars are more often 

 found in the lower jaw than in the upper, and more often an the left than on the right 

 side, but this may be mere coincidence as it is not corroborated by Bateson's records. 



Selenka regards the' fourth molars of the Anthropoid Apes as »Neubildungen » 

 and concerning the cause of their appearance he utters as follows. »So gewagt es im all- 

 gemeinen ist, die Entstehung eines Organs auf die Wtrkung mechanischer Zug- und 

 I>ruckkrafte zuriickzufiihren, so diirfen solche Erklarungsversuche doch nicht von der 

 Hand gewiesen werden, wenn sie sich auf blosse Modificationen vorhandener Organan- 

 lagen beziehen. In diesem Sinne scheint es erlaubt, die Veranlassung zur Entstehung 

 neuer Zahne in der zunehmenden Verlangerung der Kief er zu suchen. Die Vergrosserung 

 der Kaumuskeln bewirkt eine Vergrosserung ihrer Ansatzflachen am Kiefer, und die 

 auffallende Verlangerung des horizontalen Astes des Unterkiefers, welche gegen Schhiss 

 des Zahnwechsels stattf indet, wird auch das Hinterende der Zahnleiste in Mitleidenschaf t 

 Ziehen konnen- und derselben Gelegenheit bieten, die ihr innewohnende Fahigkeit zu 

 entfalten, namlich Zahnkeime zu entwickeln.» The explanation thus offered appears 

 to be plausible. 



The capacity of the brain-cavity of the Chimpanzee skulls of the present collec- 

 tion has been measured by means of hemp-seed after closing fissura orbitalis etc. with a 

 little cotton, and the following results have been obtained by this. 



1 Sitz.ber. d; Egl. Akad. d; Wiss. Berlin, 1896, p. 381—392. 

 K. St. Vet. Akad. Handl. Band 58. N:o 2. 



