390 C. JUDSON HERRICK 



Fig. 1 Dorsal view of a wax model of the medulla oblongata of a 38 mm. larva 

 of Amblystoma tigrinum. X 42. The plexus chorioideus has been removed. On 

 the right side of the model the positions of the underlying motor nuclei of the 

 cranial nerves are indicated as projected upon the ventricular surface. On the 

 scales above and below the figure are given the serial numbers of the tranverse 

 sections upon which the model is based, the sections being 15m thick. Drawings 

 from 15 of these sections, which were prepared by the silver reduction method of 

 Ram6n y Cajal, are shown in figures 4 to 18. The method used produces consid- 

 erable shrinkage and distortion of the form relations, especially in the cerebrum. 

 In the medulla oblongata the tissue is of firmer texture and the distortion is less. 

 Comparison with other specimens of larvae of the same age prepared by various 

 other methods indicates that in this model the only important distortion of the 

 natural form relations is manifested by a slight exaggeration of the ventricular 

 sulci and by a partial collapse of the thin-walled caudal end of the tectum mesen- 

 cephali near the mid-dorsal line into the recessus posterior mesencephali (cf. figs. 

 5 and 6). 



Fig. 2 View of the medial surface of the same model after division in the sagit- 

 tal plane. X 42. 



