628 PEOF. H. G. SEELET ON THE CRANIAL CHARACTERS OP 



depth increases to more than 3 centimetres, and the base and roof 

 of the brain continue nearly parallel to each other for between 6 

 and 7 centimetres. The cause of the sudden anterior decrease in 

 depth is that a large nerve 8 millimetres thick is given off at the 

 anterior end of the brain, in the median line ; and this, according 

 to analogy, I regard as being the olfactory nerve (fig. 1, olf). At 

 the distance of about 6^ centimetres backward a slight angular 

 bend occurs in the roof of the brain-case, so that it increases in 

 height for the next 4 centimetres as it extends backward. This 

 part of the roof is straight ; the anterior part is very gently arched. 

 Below the point where this angle occurs is the entrance to the 

 pituitary fossa {pf). The depth from the roof of the brain-case to its 

 base is 6 centimetres. The pituitary fossa extends backward under 

 a strong forwardly directed process of the sphenoid bone, and from 

 it a canal is prolonged forward, which becomes a little narrower 

 as it extends below the canal for the olfactory nerve, from which it 

 is separated by a thickness of a centimetre of bone. This nerve I 

 regard as the optic (fig. 1, op). The base of the brain-cavity from 

 the sphenoid to the superior extremity of the basioccipital, where 

 the spinal cord enters the skull, is gently concave in length. At 

 10 J centimetres from the anterior end of the specimen a slight bony 

 process descends downward and forward from the roof of the brain- 

 case, as though to make a posterior termination to the cerebrum. 

 At this point the depth of the brain-case is about 4J centimetres ; 

 a narrow excavation appears behind this process, not more than a 

 centimetre wide, and rather compressed above, as though marking 

 the position of the optic lobe of the brain (o). Posterior to this the 

 roof of the brain-case, which is convex in length, descends rapidly 

 to the foramen magnum {FM), which is less than 2 centimetres high. 

 This constriction 1 take to indicate the relatively small si^e and de- 

 pressed shape of the cerebellum ((7*"). Posterior to the brain-cavity 

 the superior concave neural surface of the basioccipital bone {Bo) 

 extends backward for 2| centimetres ; so that, in its median line, 

 the brain-case is remarkable for the comparative parallelism of its 

 inferior and superior margins, disturbed mainly by the elevation 

 of the optic lobes and hinder part of the cerebrum and by the 

 derpression of the cerebellum. 



It will now be convenient to describe the characters shown on 

 the right side of the section, fig. 2. Notwithstanding the com- 

 parative thinness of the vertical layer which has been removed from 

 this side, the brain-case is only 11 centimetres long, showing that 

 the cerebrum must be compressed from side to side, so as to taper, 

 anteriorly at a rapid rate. The floor of the brain-case is concave in 

 length, but the concavity is divided into two principal portions— the 

 posterior one corresponding to the basisphenoid region, and the 

 anterior one, which is less regular, occupying the presphenoid 

 region. The roof of the brain- case now has two bony processes 

 extending into it ; first, the small one, already described, which has 

 not greatly altered its shape, though it is perhaps a little nar- 



