NERVOUS SYSTEM. VERTEBRATA. 295 



D. 376. The left half of the brain of a Common Seal (Phoca 



vitulina} . 



D. 377. The right cerebral hemisphere of a Common Seal (Phoca 

 vitulina), in which the whole of the lateral wall has been 

 removed to open up the lateral ventricle. 



Behind the upper extremity of the hippocampus the 

 small posterior horn of the ventricle is seen, and a bulging 

 (calcar avis) is visible upon the mesial surface. A glass 

 rod has been pushed through the calcarine (so-called 

 " splenial ") sulcus to show that the calcar avis in this 

 brain is really produced by the calcarine sulcus. This fact 

 was first recorded by Serres (Anat. Comp. de Cerveau, 

 Paris, 1826, t. ii. p. 470). 



Fish, who (in apparent ignorance of this) rediscovered 

 the presence of the posterior cornu, singularly failed to 

 appreciate its important bearing upon the question of the 

 homology of the so-called " splenial fissure," for he was 

 doubtful whether the calcarine or the parieto-occipital 

 sulcus should be regarded as its (splenial sulcus) Primate 

 representative. 



P. A. Fish, Jouru. Comp. Neurology, 1898, p. 79. 



D. 378. A cast of the cranial cavity of a Common Seal (Phoca 

 vitulina). 



D. 379. The brain of a Gray Seal (Halichcerus grypus). 

 This brain resembles that of the Common Seal. 



0. C. 1325 u a. 



D. 380. The brain of a Monk Seal (Monachus albiventer). 



The general features of this brain closely resemble those 

 of Phoca ; but in many respects it is much more like the 

 brains of Odobcvnus and Otaria than that of Phoca. It 

 is therefore of considerable value to us in bridging over 

 what would otherwise be the very considerable gap between 

 the families of the Pinnipedia. 



The pseudosylvian, suprasylvian, and orbital snlci are 

 like those of Phoca. The coronal sulcus, however, is not 

 joined to the lateral sulcus. 



