The brain of Gadus, with special reference to the medulla oblongata and its variations according to the feeding habits of different gadidæ—I

Abstract

In a previous paper (Evans, 1932) we have described the medulla oblongata of the Cyprinidae and have shown that the pattern of the medulla varies according to the habits of feeding, so that it was possible to divide the Cyprinidae into four groups. We propose to attempt a similar study of the Gadidae and it will be found that the pattern varies in a definite manner according to the methods of feeding, and the character of the food. In carrying out this research we are very much indebted to the exhaustive examination of the stomach contents by Cunningham (1896) and more recently by Borley and Thursby-Pelham (1926). Before describing the medulla oblongata in the various members of the Cod family, it is necessary to point out the marked difference in the naked eye appearance of the hind-brains of the Cyprinidae and Gadidae. In Cyprinidae the brain is characterized by the great development of the vagal and facial lobes. The vagal lobes form a pair of large swellings on either side of the rhomboid fossa and embrace between their anterior ends the unpaired facial lobe—a rounded body situated in mid line behind the cerebellum. This “lobus impar” represents apparently “a fusion of the two small facial lobes seen in the Cod” (Goronowitsch, 1897). The dorsal surface of the medulla in the Cod is occupied by a series of swellings that almost entirely close the rhomboid fossa.