EXPLANATION OF THE PLATES AND WOODCUTS. 



Bay. In No. 3. a third vein is represented, interposed between the two principal 

 veins : p. ISO. 

 Nos. 4. 3. Connexion of chalk and syenite at Torr Eskert : pp. 183, 184. 



PLATE XIV. 



Illustrates Sir Philip Grey Egerton's memoir on certain peculiarities in the cervical 



vertebra of the Ichthyosaurus: p. 187 to 193. 

 [All the figures are of the natural size except 9 and 10, which are reduced toone half.] 

 Fig. 1. Atlas of an Ichthyosaurus. 



a. Occipital socket. 



b. Articulating surface for the first subvertebral bone. 

 Fig. 2. Side view of^g-. 1. 



A. The atlas. 



B. The axis. 



a. Surface for the insertion of ligaments. 



b. c.f.g. Planes for the articulation of the subvertebral bones. 

 d. Articulation of the first rib. 



Fig. 3. Atlas and axis disunited. 



a. Articulating surface for the first subvertebral bone. 



b. Second subvertebral bone in situ. 



c. Articulation for the first rib. 



Fig. 4. Upper view of the first subvertebral bone. 



a. Surface articulating with the atlas. 



b. b. Anterior alae. 



c. Socket embracing the lower circumference of the occipital tubercle. 



d. Plane abutting against the second subvertebral bone. 

 Fig. 5. Under view oi Jig. 4. 



a. Central boss of bone. 

 Fig. 6. Lateral view of fig. 5. 

 Fig. 7. View of the cervical portion of an Ichthyosaurus. 



a. Basilar element of the occipital bone. 



b. c. d. e. f. Cervical vertebree. 

 g, h. i. Three subvertebral bones. 



k. I. Sockets for the first and second subvertebral bones. 

 Fig. 8. Three subvertebral bones seen from belovv. 

 Figs. 9. 10. Cervical vertebrae of a large Ichthyosaurus, reduced half. 



a. a. Intervertebral cavity, b. b., c. c, Alternate elevations and depressions of the 

 articulating surfaces of the bones fitting into each other. 

 Fig. 11. Third cervical vertebra of a small Ichthyosaurus. 



a. Articulation for the third subvertebral bone. 

 Fig. 12. Atlas and axis of Ichthyosaurus tenuirostris from Street, in Somersetshire. 



a. Articulation for the first subvertebral bone. 



b. Second subvertebral bone in situ. 



c. Sharp edge of the axis, showing the non-existence of the third subvertebral bone 



in this species. 



