Herrick, Organs of Smell and Taste. 163 



the physical stiniuh and the psychical quahties of odors and 

 savors, especially in the higher vertebrates; but these are in all 

 animals quite subordinate to the type of reaction involved. 



A critical examination of the central conduction paths for smell 

 and taste supports this view of the case. The central olfactory 

 apparatus is very constant throughout the vertebrate phylum. 

 The organ of smell, as befits a distance receptor, is located in the 

 leading segments and its central connections are with the extreme 

 tip of the neural tube; indeed in all of the true vertebrates it has 

 grown out rostrad beyond the primary neural tube, the entire 

 rhinencephalon lying in the telencephalon, or ultra-terminal brain. 

 The path extends from the olfactory bulb to the tuberculum olfac- 

 torium and other structures in the base of the forebrain, thence 

 directly back to the olfactory centers in the thalamus or else first 

 to the olfactory cerebral cortex (hippocampal formation, etc.) 

 and then to the thalamus. The two principal olfactory centers in 

 the thalamus lie in the epithalamus and hypothalamus respectively. 

 Each of these thalamic centers receives in higher vertebrates olfac- 

 tory tracts from both the basal and cortical olfactory centers of 

 the forebrain; and each sends a strong tract to reach the motor 

 centers. These tract's are the tr. habenulo-peduncularis (fasc. 

 retroflexus or bundle of Meynert) and the fasciculus pedunculo- 

 mammillaris (tr. mammillo-bulbaris). In lower vertebrates both 

 of these tracts can be traced far downward into the medulla oblon- 

 gata, where they come into relation directly with the motor nuclei 

 of the cranial nerves and the evidence is that either directly or 

 indirectly they pass still farther into the spinal cord for the somatic 

 motor reflexes characteristic of olfactory reactions. 



The central gustatory path is well known only in fishes. Here 

 there are much more direct reflex connections with the visceral 

 motor nuclei of the cranial nerves than the olfactory system shows, 

 and in most fishes no important connections with somatic motor 

 nuclei save by way of the hypothalamus and tractus mammillo-bul- 

 baris. There are certain fishes, however, in which taste buds have 

 been developed secondarily in the outer skin of the general body 

 surface. Here they have been shown to function as exteroceptors* 

 and in these cases the central connections of the cutaneous taste 



* C. JuDsoN Herrick: The organ and sense of taste in fishes. Bui. U. S. Fish Commisssion for igo2, 

 fVashington, ig04. The central gustatory path in the brains of bony fishes. Journ. Comp. Neurol, 

 and Psych., vol. 15, no. 5. 1905. 



