ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 421 



of the cerebellum. In a general way, disregarding certain 

 sets of fibers the cerebellum and the pons may be compared 

 to a signet ring, the band of which is the pons, the signet 

 being the large cerebellum itself, the finger the cord pass- 

 ing between. It is well to repeat again that this analogy is 

 not quite true either anatomically or physiologically, but the 

 detailed course of the fibers at this point will be followed in 

 a succeeding chapter. 



Immediately back of the pons is the medulla, with its 

 widest portion near the pons and gradually tapering back- 

 ward until it reaches the size of the cord into which it 

 gradually blends. Along the pons and the medulla arise the 

 remaining cranial nerves. 



While all of these structures at the base of the brain 

 have been described in connection with the cerebrum, some 

 belong to the mid or hind-brain in reality. The fore-brain 

 extends to the beginning of the crura cerebri and the 

 mid-brain as seen from below includes the crura cerebri, 

 while the hind-brain consists of the pons, medulla oblon- 

 gata and cerebellum. If by means of the fingers the cere- 

 brum and cerebellum be pushed apart by tearing away the 

 brain coverings which hold them in place, here, the dorsal 

 view of the mid-brain appears. This is marked by four 

 hemispherical eminences called the corpora quadrigemina. 

 Of these the anterior pair is much larger and is called the 

 nates, the posterior pair the testcs. These corpora quadri- 

 gemina occupy on the dorsal side of the mid-brain the posi- 

 tion held by the crura cerebri on the base. If the cerebrum 

 and the mid-brain be torn apart somewhat, there will be 

 seen lying, just anterior to the corpora quadrigemina and 

 on the median line of the body, a small gland-like structure 

 about the size of a pea or smaller, known as the pineal 

 gland. This pineal gland is not connected with the mid- 

 brain at all, but arises from the two optic thalami lying 

 immediately anterior. This structure was the object of some 

 speculation formerly when the view was advanced that being 

 the only unpaired structure in the brain it must be the seat 



