iNO.1325. CEREBRAL FISSURES OF THE WALRUS— FISH. 685 



appear at all in the floor of the ventricle. A slight caudal projection 

 (of the cavity, at the beg-inning of the medieornu, extending- just 

 I beyond the level of the splenial fissure, represents the postcornu. In 

 his dissection of the walrus brain, Turner shows no indication of a 

 t postcornu, but in the text he states: "Where the cavity of the ven- 

 tricle curved downward and outward into the horn, an indication of a 

 recess was seen in its posterior horn, but it did not amount to a cornu 

 and there was no elevation which could be called a hippocampus minor." 

 In Ursus there is no postcornu. In Callorhinus a slight caudal spur of 

 the cavity indicates its position. Zalophus was not examined in this 

 region. In Monachus there is a fairly well-developed postcornu. 

 Murie describes a well-developed postcornu in the Manatee and Otaria, 

 and in both a well-developed hippocampus minor or calcar. In Phoca 

 mtuVina the postcornu is relatively large, and the hippocampus minor 

 is well developed, being correlated with the splenial fissure and making 

 of it, for a portion of its course at least, a total fissure. 



Terminology. — A diflicult}" of some importance is the selection of 

 the terms to be employed in the description of the fissures and gyres, 

 particularly in the brain of the Pinnipedia, where the literature is not 

 especially abundant. The literature on the carnivorous brain is more 

 extensive, but as many authors have employed terms of their own 

 without reference to the nomenclature used by others, some confusion 

 has naturally resulted. It has therefore seemed best in the present 

 case not to follow the terminologv of an}" one author, but to use those 

 terms which, b}^ their special fitness, seemed most appropriate. On 

 this account the priority of terms has not been especially considei'ed, 

 for in some cases later investigations have shown that some of the 

 earlier terms were not the best to use in considering the homologies 

 between the various forms. 



Some of the more common synonj'ms of the names of the various 

 fissures used in this article are as follows: The supersylvian is very 

 commonly called the suprasylvian. Turner and Gratiolet have appar- 

 ently confused this fissure with the lateral in Phoca. I have preferred 

 the term postsupersylvian, as used by Krueg, Turner, and others, to 

 postsylvian. as recommended by Owen and Wilder. The term pre- 

 supersylvian has been introduced to appl}' to what is conmionl}" 

 described as the anterior or frontal portion of the supersylvian or the 

 ectosylvia antica of Ziehen. The superorT)ital of Flower and A^"ilder 

 is preferred to the intraorbital of Turner and Langley . This fissure has 

 also been designated as the presylvian by Krueg and others. The 

 term presylvian has also been applied ])y some writers to describe what 

 commonly appears to be the coronal fissure. Cruciate is retained, as is 

 done by most writer's, although frontal fissure is the term originally 

 suggested by Owen. I have also employed the tei-m marginal fissure, 

 as used by Owen and Wilder, instead of suprasplenial, as used by Krueg 

 and Turner. 



