26o GENERAL ORNITHOLOGY part ii 



white substance (pons Varolii, peduncles, etc.) and the holloAv under- 

 neath it (" fourth ventricle ") constitutes the epencephalon of most 

 writers, by some called the metencephalon, or "after-brain." The 

 hind part of it tapers off into the spinal cord ; this tapering part 

 is the medulla oblongata, or " oblong marrow," also called the myelen- 

 cephalon, or " marrow-brain " (and by some the metencephalon). This 

 description is pertinent to brains at large, representing the general 

 plan of structure ; any fairly developed encephalon shows the parts 

 specified ; and the most complicated brain, that of man, only shows 

 what elaborate finishing touches may be given to the simple struc- 

 ture thus outlined, Avhen cells, both white and gray, but especially 

 the latter, are profusely furnished, to the ornamentation of the 

 mind's estate with race-tracks great and small, and the place of for- 

 nication, — fruits of the olive, and of the arbor vitse. The mem- 

 branes, or meninges, which hide all this from the uninitiated, are 

 three. The pia mater, or "tender mother," which immediately 

 invests the brain, is very vascular, and furnishes the blood supply ; 

 not only by small arteries which immediately penetrate the substance 

 of the brain, but by enfolded sheets which enter the ventricles, and 

 are called choroid plexus. The arachnoid, or " cobweb," comes next ; 

 a serous fluid which it secretes bathes the brain, and meets con- 

 cussion with its gentler fluctuation. The dura mater, or " stern 

 mother," is a dense outer membrane which enwraps and holds the 

 whole firmly. These meninges descend into the spinal column, and 

 answer the same purpose there, maintaining the same disposition 

 around the spinal cord. 



The Bird's Brain ofters the following comparative characters : It 

 is compact, having nothing of the straggling apart of its elements 

 seen in low vertebrates, and completely fills the cranial cavity. Its 

 long axis is about transverse to the axis of the spinal column. The 

 cerebral hemispheres are Avell developed, but do not cover the cere- 

 bellum or optic lobes ; from their dome the rhinencephalon protrudes 

 like a porte-cochere. Their surface is c[uite smooth (devoid of the 

 gyri and sulci of most mammalian brains) ; even the Sylvian fissure 

 is barely indicated. The optic lobes are of immense size, relatively 

 to those of higher vertebrates, and relatively to the rest of the en- 

 cephalon ; they appear much loosened from their surroundings, at the 

 sides and lower part of the mid-brain ; they retain their ventricles, as 

 does also the rhinencephalon. The corpora striata are very large. 

 The fornix is rudimentary. The cerebellum is Avell developed and 

 deeply sulcate, with transverse fissures, but is not divided into right 

 and left lobes ; a " fleecy " lobule on each side, the flocculus, is well 

 defined, and received in a special recess of the inner wall of the 

 skull. Parts of the medulla oblongata notable in mammals are 

 obscure or obsolete. There is no pons Varolii, or superficial trans- 



