The Anatomy of Chlamydoselachus 473 



THE BRAIN 



Garman's brief description (1885.2, pp. 16-17) of the brain of Chlamydoselachus, 

 illustrated by his Pis. XV and XVI (my Plate VI) is the first, and remains the most 

 comprehensive account of the form and structure of this organ. This comparative neglect 

 may be partly explained by the fact that it appears to be very difficult to obtain specimens 

 in which proper attention has been given to the preservation of the brain. Garman 

 states that the brain of his specimen was very soft. When removed from the skull, it 

 collapsed and spread out, so that the figures sketched are a trifle more broad and flattened 

 than is natural. His entire description follows : 



The brain is very small. Comparatively the amount of forebrain is much smaller than 

 in the higher sharks, Carcharias, Zygaena, and others. In outHnes and proportions there is 

 great similarity between this brain and that of the Notidanidae. In both of the genera of 

 that family the brain is equally elongate and the disposition of the nerves is not greatly 

 different; the differences are mainly in details rather than in general build. . . . The olfactory 

 lobe is shorter than that of Hexanchus (compare Maclay, Das Gehirn der Selachier, Plate 

 II). The olfactory bulb is similar in shape in these genera; it is a club-shaped expansion 

 with lobules at the end from which the nerve distribution takes place. Being broader in 

 front, the hemispheres taper more toward the hypophysis than is the case in Hexanchus. As 

 in the latter, the optic lobes are rounded above and in front, and are — when viewed from 

 above — about half exposed. 



The cerebellum is of medium size, rather smooth on its upper surface, rounded in front, 

 and presents an acute angle — with blunted apex — between the corpora restiformia. On the 

 upper surface the longitudinal depressions are partly due to the uneven floor of the ventricle, 

 on which the upper walls rest. There are three moderate transverse depressions. In the 

 cerebellum the amount of pHcation is greater than that in Hexanchus as figured by Maclay. 

 There is some likelihood that his figure is taken from a young specimen, and that a large one will 

 be marked by greater complication. In Maclay's figure of Hexanchus the folds are represented 

 by a simple upward line with a transverse bar on the top, like a letter T. To represent the 

 same section in the new shark, we shall have to place another T on each end of the transverse 

 bar. Maclay figures a longitudinal section of the cerebellum of a young Mustelus, which 

 shows a pretty close agreement. An adult Mustelus, which is a great deal more complex, 

 is also figured. 



The corpora restiformia are comparatively large; they approach each other behind the 

 cerebellum till there is but a small space between them. 



The medulla is large, somewhat larger than the same portion in the Notidanidae. The 

 waved appearance in the sinus rhomboidalis, fourth ventricle, is caused by the transverse 

 bands of fibers in its membranous roof. . . . 



The close similarity existing between the brains of Chlamydoselachus and the Notidan' 

 idae is a strong point in favor of genetic relationship. 



From the report on an address by Wilder (1905) before the American Philosophical 

 Society, I quote the following: 



Here [in Chlamydoselachus] the walls of the forebrain are thinner and less differen- 

 tiated [than in Scymnus], and in the lateral extensions toward the olfactory cups ('nostrils') the 

 so-called cerebral portion expands nearly equally in every direction from the axis represented 

 by the olfactory crus; in most other sharks and in rays or skates the special cerebral extension is 



