1903.] 



The Brain of the Archceoceti 



329 



Cetacea. There are no characters of the brain of the modern 

 Cetacea which can be regarded as certainly distinctive, if we put 

 aside such features as the extreme dwindling of the olfactory 

 apparatus, and the enormous development of the neopallium. Both 

 must be regarded as late acquisitions, not to be expected in an Eocene 

 mammal. Under these circumstances these slight points of positive 

 evidence of the relationship of the Archaeoceti and Cetacea must be 

 allowed some value, as reinforcing the testimony of the skeletal parts. 



If we seek to institute closer comparisons between the brain of 

 Zeuglodon and of the Odontoceti and Mystacoceti with a view to the 

 determination of its relationships, we are not unnaturally doomed to 

 disappointment. It might, perhaps, be supposed by some anatomists 

 that the absence of an olfactory bulb in the Odontoceti might point 

 to a closer affinity of Zeuglodon to the Mystacoceti, in which a small 

 olfactory apparatus is retained. But there is every indication that 

 the olfactory apparatus of the Odontoceti has become aborted quite 

 recently. 



Thus in a specimen of the embryonic brain of the Narwhal (Monodon), 

 which was given to me some years ago by Professor Howes, the remains 

 of the olfactory bulb (fig. 3, h.o.) are still quite visible as a small umbili- 



FiG. S.^Ventral aspect of brain of an early fcetus of Monodon. Natural size, 

 a.d., locus perforatus (desert region) ; b.o., bulbus olfactorius ; I.p., lobus 

 pyriformis. 



cate area in part of the " desert region " of Broca (fig. 3, a.d.), 

 wherefore it follows that in the early embryo the olfactory bulb and 

 peduncle develop as in all other mammals. Moreover, in all Odontoceti 

 traces of the pyrif orm lobe are found even in the adult ; and in the 

 brain of Kogia Greyi the rhinal fissure and the typical (macroscopically 

 only) pyrif orm lobe are retained in a form as clearly defined as that 

 of any macrosmatic mammal (fig. 4). Professor Haswell, in describing 

 this brain* emphasises the fact that "the most remarkable feature of 



* W. A. Haswell, "On the Brain of Grey's Whale (Kogia Greyi)," 1 Linnean 

 Society of New South Wales Proc.,' vol. 8, 1883 (publ. 1884), pp. 437—439, 

 pi. XXI. 



