VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 33/ 



cerebrum is not great, and in this tribe it is still less; yet not so small as in the 

 bird, &c. 



The whole brain in this tribe is compact, the anterior part of the cerebrum 

 not projecting so far forwards as in either the quadruped or in the human subject; 

 neither is the medulla oblongata so prominent, but flat, lying in a kind of hollow 

 made by the 2 lobes of the cerebellum. The brain is composed of cortical and 

 medullary substances, very distinctly marked; the cortical being in colour, like 

 the tubular substance of a kidney; the medullary very white. These substances 

 are nearly in the same proportion as in the human brain. The 2 lateral ventri- 

 cles are large, and in those that have olfactory nerves are not continued into 

 them as in many quadrupeds; nor do they wind so much outwards as in the 

 human subject, but pass close round the posterior ends of the thalami nervorum 

 opticorum. The thalami themselves are large; the corpora striata small; the 

 crura of the fornix are continued along the windings of the ventricles, much as 

 in the human subject. The plexus choroides is attached to a strong membrane, 

 which covers the thalami nervorum opticorum, and passes through the whole 

 course of the ventricle, much as in the human subject. The substance of the 

 brain is more visibly fibrous than I ever saw it in any other animal, the fibres 

 passing from the ventricles as from a centre to the circumference, which fibrous 

 texture is also continued through the cortical substance. The whole brain in 

 the piked whale weighed 4 lb. 10 oz. The nerves going out from the brain, I 

 believe, are similar to those of the quadruped, except in the want of the olfactory 

 nerves in the genus of the porpoise. 



The medulla spinalis is much smaller in proportion to the size of the body 

 than in the human species, but still bears some proportion to the quantity of 

 brain ; for in the porpoise, where the brain is largest, the medulla spinalis is 

 largest ; yet this did not hold good in the spermaceti whale, the size of the 

 medulla spinalis appearing to be proportionally larger than the brain, which was 

 small when compared to the size of the animal. It has a cortical part in the 

 centre, and terminates about the 25th vertebra, beyond which is the cauda 

 equina, the dura mater going no lower. The nerves which go off from the 

 medulla spinalis are more uniform in size than in the quadruped, there being no 

 such inequality of parts, nor any extremities to be supplied, except the fins. 

 The medulla spinalis is more fibrous in its structure than in other animals; and 

 when an attempt is made to break it longitudinally, it tears with a fibrous 

 appearance, but transversely it breaks irregularly. 



The dura mater lines the skull, and forms in some the 3 processes answerable 

 to the divisions of the brain, as in the human subject; but in others, this is 

 bone. Where it covers the medulla spinalis, it differs from all the quadrupeds I 

 am acquainted with, inclosing the medulla closely, and the nerves immediately 



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