THE BHAIN OF MAMMALS AND THE OLFACTOHY APPARATUS. 



233 



In the vertebrate series arcuate fissures occur more frequently than any 

 other. On the richly convoluted brain of the narwhal they form the type of 

 the entire fissuration (Fig. 146). 



They are numbered, counting from the Sylvian fissure out, as the first, 

 second, etc., arcuate fissure, or they are also named as; fissura ectosylvia, 

 fissura suprasylvia, etc. On the brain of the dog, which here follows, a 

 number of these fissures are again recognized from the form and the loca- 

 tion. At the posterior boundary of the frontal lobe a short sulcus passes 

 downward in a vertical covirse: the fissura, cruciata. It probably corresponds 

 to the fissura centralis; yet the identity of the two fissures is not undisputed. 

 As was mentioned in the second chapter, the brains of many animals are 

 entirely smooth. On others there are found only slight indications of sulci. 

 On many brains — for example, those of the horse and the cow — the arcuate 

 type is only distinct in the territories lying next to the Sylvian fissure — 

 toward the edge of the brain the fissiires have a more sagittal course. It 



Fig. 147. — Brain of a dog. The frontal lobe is shaded. 



would be too much of a digression to mention what is at present known con- 

 cerning the direction of the sulci in the various classes of animals. The 

 examples given are only intended to illustrate certain types and to serve as 

 an introdiiction to studies of your own. 



Our knowledge of the course of the convolutions of the brain comes from the 

 investigations of Burdach (median surface), Leuret, Gratiolet, Meynert (comparative 

 anatomy), Bischoff, Eoker, and Pansch (growing and adult brain). Moreover, there 

 exist numerous investigations on separate regions of the brain: on the gyri running 

 near the margin of the brain by Broca and Zuoherlcandl ; on the frontal gyri by 

 Wberstaller and by Herri ; on the insula by Guldberg ; further, accurate studies on 

 the development and course of single fissures by Riidinger, Gunningham, and others. 

 Besides this we possess very many monographs on the brain-surface of various mam- 

 mals; on anthropoid apes by BiscJioft, Waldeyer, and others; on lemurs by Flower 

 and Gervais ; on whales by Guldherg, Ziehen, and Kukenthal ; on ungulates by 

 Krueg, Ellenherger, Tencliini, and Negrini; on carnivorous animals by Meynert, 



