MAMMALIA. 



123 



base of the brain ; posteriorly and internally it is connected with the inferior portion 

 of the hippocampus ; anteriorly, it occupies much of the base of the anterior lobe, and 

 very little more than the large bulbous extremity of the nerve is detached. In the 

 porpoise there is no appearance of the olfactory nerves or of the continuations of the 

 great hippocampus. The commissure of the optic nerves is generally less broad than 

 in man. The crura of the brain in the horse are large and appear long, as the small 

 size of the annular tubercle leaves them more exposed ; they are longer in the goat 

 and sheep than in the dog and fox ; the origin of the third nerve is nearly the same ; 

 the cribriform lamina hardly exists, and the mammillary eminences vary in appearance, 

 being frequently, as in the horse and others, more like a single indistinct prominence. 

 The pituitary gland is usually large, especially in the horse, and appears to be com- 

 posed of two substances, which resemble the cerebral matter and the renal capsule. 



The cerebellum varies in form and size, but the lateral lobes, however small, may 

 generally be compared with those of man ; and the middle, however large, with the 

 vermiform processes. But it varies in the greater or less proportion of the lateral 

 lobes to the middle, generally in the less ; in the porpoise, however, the lateral lobes 

 are nearly as large, and the middle as small, as in man ; and in many instances it 

 varies in the presence of lateral lobules attached at the outer side of the inferior portion 

 of the lateral lobes, as in the simise and the rat, and these correspond with the 

 rudiments of lateral lobes in birds, and are fitted into similar cavities, left by the less 

 close adaptation of the surrounding bone to the semicircular canals. It varies in the 

 different shape of the lobes, in their being placed more or less backwards, and more or 

 less underneath the posterior lobes of the brain, and consequently in having their 

 superior parts more or less exposed. The convolutions also vary, and are thicker and 

 shorter in some, narrower and longer in others, but there is the utmost variety in their 

 shape and mode of aggregation for producing the general form of the whole cerebellum. 



The annular tubercle is much less than in man ; it however corresponds with the 

 size of the inferior pedicle of the cerebellum, of which it appears to be the con- 

 tinuation, whilst the crura of the brain are more proportioned to the size of the oblong 

 medulla: in the porpoise it is very large. In many of the mammalia a band of 



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