STRUCTURE OF BIRDS. 49 



transversely grooved, and formed almost entirely of the middle 

 lobe, which in the mammifera is comparatively small. In the 

 posterior view, Fig. 8, are seen, besides the cerebral lobes «, «, 

 and the cerebellum, ^, the oval bodies, c^ c^ named optic lobes, 

 analogous to the corpora quadrigemina in man, and situated 

 between the cerebrum and cerebellum beneath ; together with 

 the medulla oblongata^ d, a large uniform mass placed beneath 

 the cerebellum and behind the optic lobes. In Fig. 9, repre- 

 senting the base of the brain, the same parts are seen, namely, 

 the cerebrum, a, a^ the cerebellum, 6, the optic lobes, c, c, and 

 the medulla oblongata, c?, which is observed to be destitute of 

 the prominences seen upon it in the mammifera. The nume- 

 rals refer to the cerebral nerves. The first pair, or olfactory^ 1, 

 come off from near the anterior extremity of the cerebral lobes, 

 pass along the septum of the orbits, and are distributed upon 

 the pituitary membrane of the upper spongy bone. The second 

 pair, or optic nerves, 2, are remarkably large, and unite so as 

 apparently to be perfectly incorporated. Of the rest it is un- 

 necessary to speak. The spinal marrow is generally of great 

 length, and has two dilatations or enlargements, corresponding 

 to the origin of the nerves of the wrings and legs. The posterior 

 enlargement is generally greater than the anterior, more decided- 

 ly so in those birds which do not fly. The spinal nerves cor- 

 respond in number to the vertebrae, and therefore vary exceed- 

 ingly. The brachial plexus is formed by the last two cervical and 

 first two dorsal nerves ; and the nerves of the posterior extremi- 

 ties are furnished by the posterior lumbar and the sacral nerves. 



An intelligible description of the organs of sensation would 

 occupy more space than can be devoted to the subject here ; 

 and as my object is to bring into notice certain parts which 

 have been too little regarded by ornithologists, not to present 

 an elementary treatise, I shall merely offer a few remarks on 

 them, reserving the exposition of the eye and the ear especially 

 for the convenient opportunities which will be presented when 

 I come to treat of the Hawks and Owls. 



The eyes of birds are remarkable for their great size, for the 

 convexity of the cornea, for having the sclerotic coat formed 

 anteriorly by a circle of bony plates, and for the existence of a 



E 



