312 



NERVOUS SYSTEM OF VERTEBRATES. 



a short distance in front of the nucleus habenulae. Its nervous 

 nature is evident in embryos but in the adult it has been confused 

 with an entirely different structure under the name of paraphysis. 

 In the accompanying Figure 152 the relations of the so-called 

 paraphysis of a monotreme (Omithorhynchus) are compared 

 with those of the caudal part of the epistriatum in a tailed amphib- 



Fig. 153. — A sagittal section of the forebrain and interbrain of a chick embryo 

 of 7.0 days. From Minot. F.B., forebrain; M.B., midbrain; chi., optic chiasma; 

 ep,, epiphysis; hy., hypophysis; Inf.g., infundibular gland (saccus vasculosus); 

 P., paraphysial arch; Par., paraphysis; p.c, posterior commissure; V, velum. 



ian (Necturus). The structure which is properly known as the 

 paraphysis is in lower vertebrates an outgrowth from the mem- 

 branous roof of the forebrain in front of the velum transversum 

 (Figs. 36, 147 and 153). 



The limits of the secondary and tertiary olfactor}^ centers in 

 amphibia are not clear but the dorso-medial and dorso'-caudal 



