OF NATURAL HISTORY. 51 



yellow coagulum gradually forms in one of them", which increafes 

 till its coat difappears. It then changes into a hemifpherical body 

 called corpus luteum, which is defcribed as being hollow and con- 

 taining within its cavity very minute eggs, each of which, it is fup- 

 pofed, may be impregnated, and produce a foetus. After impreg- 

 nation, one of thefe eggs, as we are informed by anatomifts, is ab- 

 forbed by and paffes through the Fa lopian tube into the uterus, 

 where it is nouriflied till mature for birth. 



We fliall conclude this fubjedt with a concife account of the in- 

 ftruments of fenfation. The organs hitherto defcribed convey no- 

 thing more than the idea of an automaton, or felf-moving machine- 

 But fenfaiion, or the perception of pleafure and pain, is cfTedcd by 

 organs of a peculiar kind. Thefe organs are all comprehended un- 

 der the general appellations of the brain and nerves. 



Befide the bones of the cranium, the brain is invefted with two 

 membranes, csMed dura z.nd pia mater, becaufe they were fuppofed 

 by the Arabians to be the fource of all the other membranes of the 

 body. Under the denomination of brain are comprehended three 

 diftincfl parts, the cerebrum, the cerebellum, and medulla oblongata. 

 The cerebrum is a foft medullary mafs, fituated in the anterior part 

 of the flcull, and divided, by a portion of the dura mater, into two 

 hemifpheres. It confifts of two fubftances, the cortical, which is 

 greyifh, and the medullary, which is fofter, and of a very white co- 

 lour. The cerebellum is divided into two lobes, and its fubftance is 

 firmer and more compaft than that of the cerebrum. It is likewife 

 compofed of the cortical and medullary fubftances. The reunion of 

 the medullary fubftances of the cerebrum and cerebellum, at the 

 bafis of the fkull, forms xht medulla oblongata, of which the fpinal 

 marrow is a continuation. The brain of the human fpecies is pro- 

 portionally much larger than that of quadrupeds. 



G 2. The.: 



