BRAIN AND ORGANS OF SENSE. 731 



lateral halves as yet developed which in the higher Mammalia assume 

 such size and importance ; the corpus callosum and fornix are both 

 wanting, a simple commissure being still sufficient. Neither has the 

 cerebellum in these animals assumed its complete development, pre- 

 senting only the central portion ; so that the pons Varolii, or the great 

 commissure which in Man unites the lateral cerebellic lobes, is of course 

 deficient. The olfactory and optic lobes are even here recognizable as 

 distinct elements of the cerebral mass, and the origins of the nerves 

 strictly conform to the arrangement already described in the brain of 

 Reptiles. The rest of the cerebro-spinal axis presents no peculiarity 

 worthy of special notice ; and the general distribution of the cerebral 

 and spinal nerves is so similar in all the Vertebrata, that it would be 

 useless again to describe them in this place. 



(2073.) The sympathetic system in Birds is well developed, and its 

 arrangement differs in no essential particular from what is seen in the 

 human body : the situation of the cervical ganglia is, however, peculiar, 

 inasmuch as they are lodged in the bony canal formed by the transverse 

 processes of the vertebrae of the neck for the reception of the vertebral 

 artery, and are thus securely protected, in spite of the unusual length 

 and slenderness which the neck not unfrequently exhibits. 



(2074.) But if in the general arrangement of the nervous system of 

 the feathered races there is little to arrest our notice, we shall find in 

 the construction of the organs of their senses many circumstances of con- 

 siderable interest to the physiological reader ; and consequently these 

 will require a more extended description. 



(2075.) The sense of touch must obviously be extremely imperfect in 

 these animals : their body, enveloped in feathers, can be little sensible 

 to impressions produced by the contact of external objects ; and their 

 limbs, covered as they are with plumes, or cased in horny scales, are but 

 little adapted to exercise the sense in question. The beak alone offers 

 itself as calculated to be a tactile instrument ; but even this, enclosed as 

 it is in the generality of birds by a dense corneous case, must be very 

 inefficient in investigating the outward surfaces of substances ; never- 

 theless in some tribes the beak is undoubtedly extremely sensitive, and 

 is used to search for food in marshy soils, or to find it in the mud at the 

 bottom of shallow waters. This is the case, for instance, in many of the 

 long-billed "Wading Birds, and also in the flat-billed aquatic families, 

 such as the Goose and Swan ; in these, in fact, the covering of the beak 

 is comparatively soft, and the nerves that supply it, derived from the 

 fifth pair, are of very considerable size. 



(2076.) As we advance from the lower to the more highly gifted 

 races of the animal creation, taste is evidently one of the last indulgences 

 granted ; and even in Birds it is only necessary to inspect the structure 

 of the tongue in order to be convinced that they can derive but small 

 enjoyment from this source. The skin of the tongue in these creatures 



