I04 ALUS. [Vol. XVIII. 



here thick and articulates dorsally with a correspondingly thick- 

 ened part of the exoccipitale. The edges of both bones are hol- 

 lowed out, and enclose, with the bones of the opposite side of the 

 head, a median nodule of cartilage (Fig. 8). 



The outer surface of the occipitale laterale presents three por- 

 tions lying in planes nearly at right angles one to the other. The 

 anterior portion is presented ventro-laterally, the middle one dorso- 

 posteriorly, and the posterior one dorso-laterally. These three 

 surfaces are not well shown in the figures, but will be readily 

 understood by comparing Figs. 7 and 10. Fig. 7 shows the an- 

 terior and posterior surfaces, Fig. 10 the middle one, this 

 last surface wrongly appearing in Fig. 7 as the posterior edge 

 of a slight ridge. The ventro-lateral surface is fiat and 

 triangular in shape. Its ventral edge is nearly horizontal in 

 position, and the bone is here thin in front and thick behind. 

 The thin anterior portion rests upon the thin lateral edge of 

 the saccular groove on the dorsal surface of the basioccipital, and 

 forms the dorsal part of the lateral bounding wall of the groove. 

 The thick posterior portion rests upon the small, inclined and 

 slightly raised surface on the solid hind end of the basioccipital. 

 From the anterior end of the mesial edge of this posterior portion 

 a delicate spine-like process runs directly forward, and, resting 

 upon the dorsal surface of the basioccipital, forms a small part of 

 the mesial wall of the hind end of the saccular groove. The cen- 

 tral part of the inferior surface of the thick hind end of the bone 

 seems to be partly cartilage, as if the ossification of the bone were 

 not complete. This condition is still more marked on two thick- 

 ened portions of the anterior edge of the bone, the bone in all these 

 places presenting somewhat the appearance described by Vrolik as 

 perichondrosteal (No. 76, p. 237). 



The anterior edge of the ventro-lateral surface of the bone is 

 slightly convex, the centre of the circle being approximately the 

 vagus foramen ; that foramen lying slightly in front of the ventro- 

 posterior corner of the surface, and at about the middle of the 

 total length of the bone. Along the dorso-posterior edge of this 

 foramen there is a short, sharp ridge, and the foramen itself is 

 sometimes separated into two parts by a thin bony partition. A 

 little in front of, and usually slightly below the vagus foramen is 



