230 BULLETIN OP THE UNIVERSITY OF WISCONSIN. 



for in forms below the mammals we have no pons to mark a di- 

 viding line. 



This is the longest part of the brain, being one and one-half 

 times as long as the rest of the brain. The metencephalon ex- 

 tends from the mesencephalon in front to the first pair of spinal 

 nerves and is of the triangular shape common in the lower ver- 

 tebrates. From its rounded base at the mesencephalon it grad- 

 ually narrows toward the spinal cord. On the dorsal surface, 

 PI. 12, we see a deep triangular fossa, the fourth ventricle, 

 which is two-thirds the length of the metencephalon, its base 

 being at the anterior part of the medulla and its apex being 

 drawn out into a narrow fissure posteriorly. This cavity con- 

 nects with the Aqueduct of Sylvius anteriorly. Besides the 

 fossa on the dorsal surface there is a deep median groove which 

 corresponds to the posterior septum, and on the ventral surface, 

 one which corresponds to the anterior fissure of the cord. 



The 'Pineal Gland. This is well developed in Necturus and 

 extends forwards between the cerebral hemispheres to near their 

 center, PI. 12. It is a triangular-shaped body as seen in cross 

 section, the apex being directed ventrad. Shortly after leaving 

 the thalamencephalon it extends dorsally, becomes narrower, and 

 its anterior end is applied against the roof of the brain case. 

 Serial sections show, however, that it does not penetrate it. 



Osborn, judging from his paper on the Amphibian brain, 

 thinks that the pineal gland does penetrate the cranial roof. I 

 have not found this to be the case in the specimens I have 

 studied ; it simply flattens against the roof. The gland is solid, 

 containing no cavity. 



The Pituitary Body. This arises from the postero-ventral 

 part of the thalamencephalon and extends backwards 5 mm to 

 near the origin of the Vlllth nerve, PI. 13. After proceeding 

 a short distance it narrows, but soon widens again, thus forming 

 a slight enlargement at the posterior end, the hypophysis. The 

 pituitary body lies on the floor of the brain case and conforms 

 closely to its irregularities. 



The pituitary body is hollow as far as the hypophysis. This 

 cavity is oval in cross section and as it approaches the hypophysis 



