138 Dr Barry on the Unity of Structure 



tures ; all grades between the splendid cerebral hemispheres in 

 Man, and the mere rudiments of hemispheres in Fishes. The 

 nervous portions of the organs of sense are, in all the Vertebrata, 

 processes of the central portion of the nervous system, through 

 the Laminae dorsales (Fig. 7. x. y) ; so that, though so varied 

 in different animals, not only all parts of the central portion of 

 the nervous system, but all processes from the latter, with a 

 common origin, and the same manner of development, may well 

 bear a general resemblance to each other, in the perfect states of 

 the less, and the embryonal states of the more, elaborate animals.* 



(The nervous ganglia of the Cuttle, and perhaps of many other 

 invertebrated animals, seem to correspond, not with the sympa- 

 thetic, but with the spinal ganglia of the Vertebrata ; a spinal 

 cord and brain not being present. ) It is remarkable, that in 

 the Cuttle, there occur cartilaginous rudiments of vertebra?, un- 

 der which the ganglia lie.) 



The muscles' of the trunks in different animals of the Class 

 Vertebrata, are but modifications of the fleshy portions of the 

 Laminae dorsales and ventrales ; and the muscles of their extre- 

 mities, are only similar metamorphoses of those portions of the 

 latter, that are carried out with the osseous (or at first cartila- 

 ginous) foundation of the extremities themselves. (See fig. 8, 

 below.) 



All the resemblances in the vascular system of different ani- 

 mals, are, in like manner, referrible to a common origin, and the 

 same manner of development ; and its varieties, to various modi- 

 fications in direction (or type) and degree. 



The Mucous tube originates, as processes, the mouth, oeso- 

 phagus, stomaph, respiratory apparatus, liver, urinary bladder, 

 and other organs; in part also, and in conjunction with the 

 Vascular tube, the genital organs : which parts, in all their va- 

 rieties, bear a general resemblance to corresponding parts in 

 different animals. 



It has been said that the spinal cord originates the brain. This is most 

 untrue ; the spinal cord does not exist before the brain j but there exists a 

 central portion of the nervous system, out of which arise both brain and spi- 

 nal cord. 



f The term " brain" is here limited to the enlargement at one extremity 

 of a mass, of which the other forms a spinal cord. (Von Bar, 1. c.) 



