No. I.] THE PRIMITIVE VERTEBRATE BRAIN. cr 



Fig. I. Longitudinal horizontal section of spinal cord of Amblystoma, showing 

 the neuromeres of the spinal cord and their relation to the mesoblastic somites. Also 

 the typical nuclear and cell arrangement. Z. 4 D. 



Fig. \a. Longitudinal horizontal section of spinal cord of Triton, showing the 

 same features as in Fig. i. Z. 4 D. 



Fig. 2. Longitudinal horizontal section of spinal cord of Anolis sagrcci, showing 

 same features as in Fig. i. Z. 4 D. 



Fig. 3. Spinal cord of Chick. Longitudinal horizontal section, showing same 

 features as in Fig. i. Z. 2 D. 



Fig. 4. Longitudinal horizontal section of hind-brain of Amblystoma puncta- 

 ium, showing the five neuromeres in the hind-brain. Also the gradual transition 

 of the neuromeres of the spinal cord into those of the hind-brain; the relation 

 of the auditory neuromere {Nm VIII.) to the auditory vesicle (^aud ves), and the 

 intersomitic relation of the myelomeres to the mesoblastic somites (jnes som'). Also 

 the relation of the neuromeres to the origin of the V., VIL, VIIL, IX., and Xth 

 nerves. Z. 2 A. 



Fig. 4a. Longitudinal horizontal section of a slightly later stage than Fig. 4, in 

 which the neuromeres have begun to degenerate. Z. 2 A. 



Fig. \b. Longitudinal horizontal section of the hind-brain of Amblystoma puncta- 

 tum, in the region of the glossopharyngeal neuromere {Nm IX.'), showing the typical 

 cell and nuclear arrangement. Z. 2 E. 



Fig. 4(r. Longitudinal horizontal section of the hind-brain of Amblystoma puncta- 

 tum, between the glossopharyngeal {Ntn IX.) and vagus (iV>« A'.) neuromeres, 

 showing the cell and nuclear arrangement between two neuromeres {Spt). Z. 2 E. 



Fig. 5. Horizontal longitudinal section of the hind- and mid-brain of Anolis 

 sagra'i, showing the six neuromeres in the hind-brain and the relation of the audi- 

 tory neuromere (jVm VIII.) to the auditory vesicle (and ves). Z. 2 A. 



Fig. 5^. Longitudinal horizontal section of Anolis sagrai, showing the six neuro- 

 meres in the hind-brain and their relation to the origin of the V., VIL, VIIL, IX., 

 and Xth nerves. 



Fig. ^b. Longitudinal horizontal section of the hind-brain of Anolis sagrwi, in 

 the region of trigeminus {Nm V.), abducens {iVm VI.), and facial {Nm VII.) neuro- 

 meres, showing the typical nuclear and cell arrangement. Z. 2 D. 



Fig. 6. Longitudinal horizontal section of the hind-brain of a five-day Chick 

 embryo, showing the six neuromeres in the hind-brain and the position of the audi- 

 tory neuromere with respect to the auditory vesicle {atid ves). Z. 2 A. 



Fig. 6a. Longitudinal horizontal section of a four-day Chick embryo, showing 

 the relation of the six neuromeres in the hind-brain to the V., VIL, VIIL, IX., and 

 Xth nerves. This section is not cut exactly in a longitudinal horizontal plane. 

 Z. 2 A. 



Fig. 6b. Longitudinal horizontal section of the hind-brain of a four-day Chick 

 embryo in the region of the neuromeres, abducens {JVm VI.), facial {Nm VII.), 

 and auditory {Nm VIIL), showing the typical cell and nuclear arrangement of the 

 neuromere facial and the septum {Spt) between the adjoining neuromeres. Z. 2 D. 



Fig. 7. Longitudinal horizontal section of the primitive fore-brain of Amblys- 

 toma punctattim, showing the two neuromeres, — olfactory (A>« /.) and optic 

 {Nm II.). Also the typical cell and nuclear arrangement of the neuromeres. 

 Z.4A. 



