36 



LECTURE II. 



bone, as it merely assists in supporting the anterior lobes 

 and can scarcely be considered as belonging to the base of the 



Fig. 3. Base of sfaill, inner siu'face; calvai-ium removed. 



a. The frontal sinuses connected with the nasal cavity. 6. The ethmoid bone, 

 with the crista galli and cribriform plate for the passage of the olfactory nerves, 

 c. Anterior fossa, roof of the orbit, d. Frontal bone. e. Anterior clinoid process. 

 /. Great wing of the sphenoid bone. g. Body of the sphenoid bone ; depres- 

 sion of the sella turcica, h. Posterior clinoid process, i. Squama of the 

 temporal bone. Tc. Body of the occipital bone. I. Parietal bone. m. Petrous 

 portion of the temporal, o. Occipital foramen, p- Cerebellar fossa, g. Occi- 

 pital squama. 



brain. The central parts, or bodies, of the occipital, sphenoid, 

 and ethmoid bones, correspond to vertebrae, which, however, 

 are considerably modified in their structure. The ethmoid bone 

 exhibits, though imperfectly, the form of a vertebra without 

 peripheral parts ; the occipital bone, on the contrary, represents 

 a perfect vertebra, having not merely articulating surfaces for 

 the succeeding vertebra, the so-called atlas, but forming the/ora- 

 men magnum, by which the continuation of the spinal cord enters 

 the cranium. The sphenoid bone finally represents an interme- 

 diate shape, its body, on the one hand, being a continuation of 



