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witli generous kindness, placed at niv «lisposal, ont of his I'ich and 

 valnable collection of enibrvos, sncii stages as Avere proper for this 

 investigation. 



In what follows a brief description will be given of the form and 

 development of the chondrocraninm as it appears at the height of 

 development; this description is based on the reconstructed waxmodel 

 which I made of the skull of an embryo of 34 mm, length. Other 

 details of this end)rvo are shown in Keirel's Normentafel ^). 



Since an extensive and illustrated description will follow elsewhere, 

 I shall be very brief here and give no detailed information as to 

 literature and comparisons. For the first and also for the nomen- 

 clature used ajid the meaning of many only shortly mentioned 

 details 1 refer to Gaupp's brilliant comparative of the development 

 history of the vertebrate cranium in Hertwig's Handbook '). 



The basal plate is broad I)ehind and well developed; anteriorly 

 it delimits the foramen magnum. It is perforated by the hypo- 

 glossus. Laterally is has a lixed connection with the ear-capsule. 

 This connection, however, is pierced by the narrow and long, almost 

 slit-shaped foramen jugulare. Behind it, starting from the junction 

 of the basal plate and the ear-capsule the cartilaginous plate de- 

 velo[»s which upwards represents the parietal plate, backwards and 

 inwards the tectum synoticum. This tectum is a very narrow strap. 

 So in this respect Tarsius resembles tiie young foetus of monkeys 

 and man (cf. Bolk, Petr. Camp. II) and differs from the other mam- 

 mals, where a broad plate is found. 



Further forwards the basal [)lale itself becomes Aery remarkably 

 narrow, so that here it consists only of a thin, round projection. 

 At the same time it is separated by long slits from the two ear-capsules, 

 with the anterior parts of which it only coalesces again in the region 

 of the sella. This thin projection rises rather steeply, and in the 

 sella region . it becomes quite considerable with its two processus 

 clinoidei posteriores. The two slits terminate close by, after having 

 grown very narrow. Their existence seems to be very rare in mam- 

 mals; they are defects which may be compared with the fenestra 

 basicranialis posterior of Reptiles (Gaupp). 



The ear-capsules themselves showed no peculiarities ; they are 



^ ') HuBRECHT und Keibel, Normentafeln zur Enlwioklung von Tarsius spectrum 

 und Nyclicebus tardigradus. Jena 1906. Tabelle N'. 36. Fig. 20 a.—c. 



I am also greatly indebted to Prof. Keibel for enabling me to use the splendid 

 series of sections of Hubrecht's Tarsius embryos on which his own investigations 

 were effectuated. 



-) Gaupp. Die Entwickhmgdes Kopfskeleltes. Hertwig's Hanilbucli 1905. Cap p. 573. 



