CHAP, xiii.] THE CATS PLACE IN NATURE. 455 



(2) The central part of the nervous system, is, throughout life, 



an elongated structure in the dorsal cylinder. 



(3) The two cylinders are, throughout life, separated hy an 



elongated solid structure the vertebral bodies or (in the 

 foetus) their cartilaginous or soft representative. 



(4) The heart is placed on the ventral side of the thus separated 



off ventral cylinder. 



(5) The anterior end of the alimentary canal bends down away 



from the nervous centres. 



(6) Limbs being present,* they are neither more nor less than four, 



and have an internal skeleton wrapped round by muscles. 



(7) There is a portal circulation. 



(8) Jaws being present, they are formed from visceral arches. 

 Were it not for the existence of a very lowly-organised fish, the 



Amphioxus or lancelet, on the one hand, and of the tunicates above 

 referred to on the other, additional distinctive characters to those 

 just given could be drawn out. For the lancelet has no distinct 

 skull, head, brain, auditory organs, chambered heart, or parts 

 formed from visceral arches, such as those we have made acquaintance 

 with. The cat then, as a backboned animal, of a type superior to 

 the lancelet, differs from all Non-Tunicate Invertebrata, not only in 

 the above enumerated characters, but also in that : 



(1) Its body is doubly cylindrical at any time of life ; 



(2) Its nervous centres are an elongated dorsal axis at any time 



of life ; 



(3) It has a vertebral column ; 



(4) It has a brain enclosed in an anteriorly expanded part of the 



dorsal cylinder, i.e., in a skull ; 



(5) It has mandibular and hyoidean arches ; 



(6) The first sign of the embryo is a medullary groove where the 



nervous centres take origin ; 



(7) Visceral clefts and arches are formed. 



10. Such being the relations borne by the cat as a backboned 

 animal to all the creatures which form the Invertebrate SUB- 

 KINGDOMS, the next point to examine is its relations to its fellow 

 Vertebrates. 



Now the sub-kingdom Yertebrata consists of three PROVINCES and 

 five CLASSES as follows : 



It consists of the province ZYGENCEpHALA,f containing one class 

 only, the class Mammalia, which is the class to which all beasts, in- 

 cluding of course the cat, belong, and of which man also (zoologically 

 considered) is a member. The province MONOCONDYLA J contains 

 two classes : the class Aves (birds), and the class Reptilia. The latter 



* This mode of expression is used 

 because many back-boned animals have 

 no limbs, and we are here considering 

 only such characters in the cat as are 

 common to every back-boned animal. 



f A term referring to the median 



union of the cerebral hemispheres by a 

 corpus callosum. 



f A term referring to the union of the 

 skull and spine by one occipital coudyle 

 only. 



