2 PEOF. OWEN ON CEREBRAL HOMOLOGIES 



to movements of parts of the mouth ; behind the " trigeminal" 

 centres are those subserving the sense of " hearing ; " above these 

 centres rises the "cerebellum." 



Thus the central masses of the neural axis in relation to the 

 " special senses " run in longitudinal sequence from before back- 

 ward, and might be called the " ganglions " of smell, sight, taste, 

 and hearing. 



These several sense-centres are not in contact with one ano- 

 ther in all Vertebrates. The olfactory ganglia are connected by 

 long cords with the optic ganglia in many fishes (Cyprinoids 

 e. g.*) . The tracts intercommunicating with the trigeminal lobes 

 recall the corresponding ones known as "oesophageal cords" 

 in Mollusks and Insects, Short and thick in all Vertebrates 

 are the tracts of the macromyelon, or " medulla oblonga," con- 

 necting the gustatory with the auditory nerve-centres ; but all 

 such centres, with superadded masses, are reckoned parts of 

 the "brain." 



The condition which afiects the length and tenuity of the tracts 

 connecting the optic (diagram, p. 13, a f) with the oral (ib. b) 

 nerve-centres in Invertebrates is the course of the alimentary 

 canal (ib. c I) neuradf, along the interspace between the fore- 

 most and the nest neural centres. 



The elongated homologues of the vertebrate " crura cerebri " 

 are termed by Lyonnet, with sound homological views, " conduits 

 de la moelle epiniere " J ; by later anatomists, rejecting his views, 

 " oesophageal cords " or " commissures." 



In illustration of the present suggestions of the homologies 

 in question, I propose to take, from the group of Arthropods, the 

 nervous system of the Locust §. 



The first, commonly foremost, neural mass (diagram, a), which, 

 by the course of the oesophagus, c, in Mollusks and Articulates, 

 is turned to the haemal aspect of the alimentary canal, is that 



* Tom. cit. p. 275, figs. 177, 178. 



t Ib. p. 276, fig. 179 {Chioncera). See also fig. 3, " On the Homology of the 

 Oonario-hypophysial Tract," Journal of the Linnean Society, Zoology, vol. x\ i. 

 p. 135. 



I 'Trait6 anatomique de la Chenille qui ronge le bois du Saule,' 4to, 

 1762. 



§ As represented in Caloptenus femur-ricbntm, C. spretus, and C. bivittatus, 

 by the exemplary dissections and microscopic sections by MM. Burgess and 

 Mason, described and figui-ed by Prof. Packard in the ' Second Eeport of the 

 U.S. Entomological Commission,' 1880, pp. 223-242, pis. ix.-xv. 



