260 O. LARSELL 



writer by various methods especially for this study. The macro- 

 scopic form and relations of the cerebellum have been determined 

 by dissections under the binocular microscope. Three species of 

 Amblystoma, namely, tigrinum, punctatum, and opacum, were 

 employed in the study. The greater part of the description is 

 based on Amblystoma tigrinum (Green). 



The external form of the cerebellum of Necturus has been de- 

 scribed and figured by Herrick in the paper previously cited. 

 Kingsbury ('95), Miller ('00), McKibben ('13), and others, in 

 descriptions or figures of the entire brain of this form, have also 

 figured and described the cerebellum in greater or less detail. 

 Other urodeles have received some attention in this respect, but 

 so far as the writer is aware, but little description has been given 

 of the cerebellum of adult Amblystoma. Stieda ('75) gives a 

 brief description of this organ and a figure of the entire brain, 

 including the cerebellum, in connection with his work on the 

 central nervous system of Siredon (Amblystoma mexicanum). 

 Osborn ('88) also figures the entire brain, with the cerebellum, of 

 the Mexican axolotl, in a study of the internal structure of the 

 brains of various urodeles, and Herrick ('14 a) figures it in con- 

 nection with a detailed study of the medulla oblongata of larval 

 Amblystoma tigrinum. 



As compared with the cerebellum of Necturus, which has been 

 described in greatest detail, this organ in Amblystoma is much 

 more massive. This massive structure continues across the mid- 

 plane, as pointed out by Herrick ('14). It forms a well-defined 

 ridge which projects dorsocaudally, from the anterior end of the 

 medulla oblongata, and which lies posterior to the points of emer- 

 gence from the brain of the IV nerve (figs. 1 and 2). Below this 

 ridge the IV ventricle extends laterally on either side to form the 

 recessus lateralis. This recess continues forward, forming a blind 

 sac which extends rostrad into the auricular lobe. This sac (fig. 

 3, d.a.) Herrick has called the anterior diverticulum. As com- 

 pared with Necturus and Amphiuma and with larval Ambly- 

 stoma, il is relatively small in the adult of the latter species. 

 It is -urrounded on all sides except posteriorly by massive tissue; 

 mesally by the corpus cerebelli and auricular lobe; dorsally and 



