468 PHYSIOLOGICAL SERIES. 



to relate, Rodent, so far as I am aware), and in all the Edentates. 

 Carnivores, Ungulates, Cetaceans, and Primates. This wide distri- 

 bution of the calcarine sulcus is not generally admitted, for most 

 writers regard the calcar avis and the calcarine sulcus as the 

 special prerogative of the Primates or even Anthropoidea, and in 

 the celebrated controversy of 1864 the late Professor Owen strove 

 to prove that it was confined to the human brain. It is, however, 

 the most primitive (it may, however, first appear at the same time 

 as the orbital and suprasylvian sulci) and widely prevalent neopallial 

 sulcus in the Mammalia. It makes its appearance in most mammals 

 (soon after the hippocampal and rhinal fissures have developed) as 

 a short oblique sulcus behind the splenium of the corpus callosum 

 (or in the corresponding situation in Marsupials), and hence it is 

 commonly called " splenial " (Krueg) in non-Primate Orders, in which 

 its true nature has not been properly recognised hitherto*. 



Its subsequent history varies greatly in different Orders. In the 

 Carnivora, Ungulata, Chiroptera, and many other mammals the sulcus 

 becomes concurrent with another element of vastly less morphological 

 importance, which I have called the ** intercalary " sulcus. The 

 calcarine-intercalary complex forms the " splenial sulcus " of those 

 brains. 



In most mammals, with the exception of the Primates, the tension 

 of the growing cortex in the infracalcarino region is relieved by the 

 downward extension of the calcarine sulcus to the neighbourhood of 

 the rhinal fissure. 



In the Anteaters, Sloths, Pangolins, Lemurs, and Apes the calcarine 

 sulcus always remains separate from the intercalary sulcus, and the 

 latter joins with the genual sulcus in the Primates to form the calloso- 

 marginal sulcus. 



In many Carnivores and Ungulates (and in large mammals generally) 

 one or more deep sulci make their appearance behind the calcarine 

 sulcus, and in most cases one of these, which we may call the " rctro- 

 calcarine" sulcus, is deeper and more constant than the others and 

 often joins the calcarine sulcus. This is seen to advantage in the 

 brain of the Lion, Tiger, or Seal among Carnivores, or in the Horse, 

 Camel, or Ox among Ungulates. This retrocalcarine sulcus is 

 obviously of very minor morphological importance in comparison \\ith 



* Meynert and Ziehen have called the splenial sulcus "calcarinr " in 

 some Carnivores, without indicating any valid reasons for tin ir \i \\s. 

 They have attempted to extend its supposed homologies to the Anthropoid 

 pattern so far as to utterly discredit any value that may attach to tln-ir 

 recognition of its calcarine nature. 



