128 THE SALAMANDER 



Comparison of the three interpretations of the meningeal coverings 



3. Brain {gross anatomy only) (PI. IX). 



The brain of the Salamander is very long compared with its 

 breadth and depth — a feature typical of Urodeles in general. Its 

 length, from the anterior end of the hemispheres to the origin of the 

 first spinal nerve, is approximately 14 mm.; its breadth, measured 

 across the posterior part of the hemispheres, is about 4 mm.; while 

 its depth, from the roof of the mesencephalon to the infundibulum, 

 is only some 3I mm. 



In dorsal v'lQw (Fig. 51), the following features are conspicuous: 



(i) The olfactory lobes. These are not fused into a median, unpaired 

 body as in the Frog, but are lateral structures which merge, without 

 any sharp line of demarcation, into 



(ii) The hemispheres of the prosencephalon^ or telencephalon. These 

 are long, cylindrical bodies with rounded ends. Together with the 

 olfactory lobes they form about 37-5 per cent, of the total length of 

 the brain, their diameter being greatest at about two-thirds their 

 length from the anterior end. They lie very close to each other 

 anteriorly, but their posterior ends turn slightly outwards from the 

 middle line. The telencephalon is followed posteriorly by: 



(iii) The diencephalon. The anterior portion of this section — the 

 thalamencephalon — is scarcely visible from the dorsal side, being 

 covered by the triangular nodus chorioideus and its associated para- 

 physis. The paraphysis develops from the anterior wall of the thala- 

 mencephalon as a dorsal evagination and becomes associated with a 

 rich vascular plexus, forming the nodus chorioideus. In the adult the 

 tissue of the paraphysis is largely confined to the posterior region of 

 the plexus. It does not penetrate the cranium but is flattened out 

 against its roof. The anterior portion of the roof of the diencephalon 

 appears at first sight to possess a median cleft. Close inspection, how- 

 ever, reveals a weak bridge of nervous material, the hahenular com- 



