CHAP, xm.] THE CAT'S PLACE IN NATURE. 465 



female. Both testes and ovaries are enclosed in the abdominal 

 cavity, and in the rook there is no urethra or prostate or Cowper's 

 glands, and no penis or clitoris, vagina or uterus, or any mammary 

 glands. No placenta of any kind is formed, but the allantois is 

 directly respiratory. It lines the egg shell, which is porous enough to 

 admit of the respiratory gaseous interchange taking place through it. 



In almost all the differences from the cat here enumerated, all 

 birds agree with the rook, whatever may be their habit of life or the 

 general external influences to which they are exposed. 



Thus the ostrich and apteryx cannot fly, and yet their pectoral 

 limb is formed on the type * of that of the crow, as also is the sub- 

 aqueous paddle of the penguin, a bird as incapable of flight as the 

 ostrich. 



17. The cat is then, as a MAMMAL, distinguished from BIRDS in 

 that: 



(1) Its skull has a "petrous bone," and a mandible formed of two 



pieces only and suspended directly from the squamosal. 



(2) Its auditory ossicles are minute and take no part in 



suspending the mandible. 



(3) There are two occipital condyles. 



(4) Its skin is furnished with hair. 



(5) Its cerebrum is large, with a corpus callosum, and its corpora 



quadrigemina are small. 



(6) Olfactory nerves being present, there is a cribriform plate. 



(7) Its ear has a complex, spiral cochlea. 



(8) Its solitary aortic arch, arches over the left bronchus. 



(9) No air-cells communicate with the lungs. 



(10) It has no syrinx, but a large and complex larynx. 



(11) Its lungs are freely suspended in the thoracic cavity. 



(12) It has a complete diaphragm. 



(13) Its posterior nares open far back within the mouth. 



(14) The ulna is larger than the radius. 



(15) The skeleton of the extremities is arranged on a different 



type. 



(16) The pelvis extends less forwards. 



(17) The ankle-joint is not an intertarsal one. 



(18) The proximal and distal parts of the tarsus do not anchylose 



with the tibia and metatarsus respectively. 



(19) The caudal vertebra) do not end in a "ploughshare f bone." 



(20) The red-blood corpuscles are not nucleated. 



(21) The right auriculo-ventricular valve is membranous only 



and not muscular. 



(22) It has no feathers. 



(23) The corpora quadrigemina are not laterally depressed. 



(24) The Eustachian tubes open separately within the alimentary 



canal. 



* In these birds the breast-bone though i f Neither do they in the extinct meso- 

 vvide is keelless. | zoic bird the Archeopteryx. 



H U 



