358 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



more evident in the rabbit than in the cat, since in the cat the fibers turn dorsally. 

 This radiating mass is called the corona radiata. 



f) Functions of the parts of the brain: As an aid in the understanding of the anatomy of 

 the brain, a few statements may be made concerning the functions of the parts identified in 

 the preceding sections. The olfactory bulbs, the olfactory tracts, the pyriform lobe, the tuber 

 cinereum, the fornix, the habenulae, the mammillary body, and the hippocampus belong to 

 the olfactory apparatus of the mammal. The olfactory impulses come along the olfactory 

 nerves into the olfactory bulbs, which are the primary olfactory centers ; they are then relayed 

 along the olfactory tracts to the pyriform lobe, which is the secondary olfactory center; 

 from the pyriform lobe they pass to the hippocampus, the tertiary olfactory center, or con- 

 scious center of smell. The hippocampus has extensive connections with other parts of the 

 brain for reflex purposes. These connections occur by way of the fimbria, a mass of nerve 

 fibers. The fimbria connects with the fornix and this in turn with the mammillary body. 

 The habenula is also connected with the hippocampus. In the dogfish practically the whole 

 of the telencephalon is concerned with smell, while here the olfactory functions occupy but 

 a part of the telencephalon, the remainder having developed new connections and functions. 

 The diencephalon is the great center of correlations in the mammalian brain. Its relation 

 to the olfactory sense has already been noted. The lateral geniculate body is the primary 

 optic center, in which, as we saw, the optic tracts terminate in part. From the lateral 

 geniculate body the optic impulses pass to the cerebral hemisphere by way of the corona 

 radiata. The pulvinar and the superior colliculus of the midbrain are also concerned in 

 optic impulses, the latter being a reflex center for these impulses. The primary auditory 

 center is located in the area acustica; from here the auditory impulses are carried, in part by 

 the trapezoid body, to the inferior colliculus and the medial geniculate body, which consti- 

 tute secondary and tertiary auditory centers. From the medial geniculate body the auditory 

 impulses are carried in the corona radiata to the cerebral cortex. In a similar way other 

 sensations such as pain, touch, temperature, pressure, consciousness of muscle and joint 

 movements, and position of the body in space are carried by definite paths (which are for 

 the most part invisible externally on the brain) to the thamalus from which they are re- 

 layed to the cerebral cortex. (The clava and tuberculum cuneatum are concerned with joint 

 and muscle sense and steadiness of body movement and position.) It will thus be seen that 

 practically all sensations make a relay in the diencephalon from which they ascend by a new 

 path, the corona radiata, to the cerebral cortex. The corona radiata is thus the great 

 pathway between the diencephalon and the cerebral cortex by means of which the sensa- 

 tions are projected, as it were, upon the cortex. It is further well known on which area of 

 the cerebral cortex each sensation is projected. After all of the sensations have thus been 

 . localized upon the cortex, there still remains a considerable portion of the cortex to which no 

 definite tracts from below can be traced. It is presumed that these areas are concerned with 

 co-ordination, reason, emotion, etc. 



The impulses toward voluntary movements originate in a definite part of the cortex, 

 pass downward in the corona radiata into the cerebral peduncles, and appear on the ventral 

 surface of the medulla as the pyramidal tracts or pyramids, which descend the whole length 

 of the spinal cord and make connections with the motor cells of the ventral columns of the 

 cord. The cerebral peduncles, besides carrying the pyramidal tracts, also carry large tracts 

 from the cortex of the pons, where they pass into the cerebellum. 



The cerebellum is the great center for equilibration and motor co-ordination. Its 

 functions are involuntary and unperceived by the conscious mind. It is connected with 

 the rest of the brain by means of its peduncles: the posterior peduncles or restiform bodies, 



