CHAP. XIII.] TEE CAT'S PLACE IN NATURE. 461 



(8) It has small corpora quadrlgemina instead of large optic 



lobes. 



(9) Olfactory nerves being present, they traverse a cribriform 



plate. 



(10) The posterior nares open far back within the mouth. 



(11) There are no gills at any time of life.* 



(12) Respiration is pulmonary only from birth. 



(13) Its heart is furnished with two ventricles. 



(14) All the blood of its body traverses the lungs. 



(15) It has but one aortic arch. 



(16) There is a complete diaphragm aiding respiration. 



(17) Its red blood-corpuscles are not nucleated, and its blood is 



warm. 



(18) The]'e are several cervical vertebrae. 



(19) In development an amnion is formed. 



(20) Kidneys replace transitory Wolffian bodies. 



All these characters serve to distinguish the Cat's class from that of 

 Fishes, as well as from Batrachians, and therefore they will also 

 serve to distinguish the cat, in so far as it is a mammal, from the 

 whole province Branchiata. 



§ 14. From amongst the creatures included in the class Reptilia (the 

 lower of the two classes which make up the province 3Ionocondy[a) 

 we may select, as a type, the common lizard [Lacerta agilis). In it 

 we find a little long-tailed quadruped, the body of Avhich is clothed 

 with horny epidermal scales. The thoracic and abdominal portions 

 of its body-cavity are not divided by a diaphragm, for it — unlike 

 that of the cat — forms no complete partition. The ribs are connected 

 with a sternum. The skull has but one occipital condyle. The 

 mandible consists of more than one bone on each side, but is con- 

 nected with the skull by one bone only — the os quadratum. This 

 bone answers to the proximal part of the cat's malleus, while the 

 part of the mandible which articulates with it answers (as it does 

 also in the Branchiata) to the distal part of the malleus. There is 

 no cribriform plate. The periotic bones unite with adjacent skull 

 bones before uniting with each other, so that they do not form a 

 " petrous bone." The limbs have the typical differentiation, and 

 the pelvis joins the sacrum. But the joint of the hind foot with 

 the leg, is not situated between the tarsus, as a whole, and the tibia, 

 as is the case in the cat. It is situated in the middle of the tarsus, 

 the proximal part of which is firmly bound to the tibia by fibrous 

 tissue, while the distal part of it is similarly bound to the meta- 

 tarsus. The phalanges of the digits are more numerous than in the 

 cat, and differ in number in different digits. There is no corpus cal- 

 losum, but there are a pair of large optic lobes. The lungs are freely 

 suspended in the thoracic cavity, but the bronchi do not branch 

 within them dichotomously. The two ventricles of the heart are 



* This and the next character do not i pipa toad, and of one or two other kinds, 

 apply in every case, as the young of the I seem never to develop gills. 



