460 THE CAT. [chap. xiii. 



limbs, eacli of whicli ends in four or five digits, and lias the typical 

 difi'erentiation. Though, without a neck externally visible, it may 

 be reckoned as having one cervical vertebra. Its body is not only 

 devoid of hair, but also of scales, and is perfectly naked and more 

 or less moist — its surface helping importantly in the respiratory 

 process. The adult has no fins, but in the young, or tadpole con- 

 dition, fins are present, but are always devoid of fin rays. Neither 

 is there any lateral line. The nostrils open within the mouth, and 

 the tympanic cavity communicates with the throat by a wide and 

 short Eustachian canal. In the adult, there are no gills, but 

 there are lungs with pulmonary arteries and veins and two auricles. 

 Nevertheless not all the blood goes through the lungs at each 

 circuit ; and there are several aortic arches. In the young there is 

 but one auricle, and there are gills and an arrangement of vessels 

 substantially as in the cod. Similarly in the young there are gill 

 arches behind the hyoidean cornua, which latter answer to the 

 anterior hyoidean cornua of the cat. In the course of deve- 

 lopment, however, these hinder gill arches shrivel into what 

 evidently represents the thyro-hyals of the cat. The blood has its 

 red corpuscles nucleated, and the cardinal veins of the young become 

 subordinate to the subsequently developed venaj cavae. The pelvic 

 limbs are attached to a pelvic girdle which joins a sacrum, but no 

 ribs articulate with the sternum. The muscles of the limbs are 

 numerous and complex. The skull has a large parasphcnoid, but 

 no basi-sphcnoid. The periotic bones coalesce. The cranium joins 

 the spine by two occipital condyles, but the basi-occipital is rudi- 

 mentary. The mandible consists of more than two bones, and it is 

 suspended to the skull by a complex suspensorium, including parts 

 representing the auditory ossicles. The same may be said of its 

 brain as has been said of the cod's. The olfactory nerves traverse 

 no cribriform plate, but there is a well-developed tympanum, though 

 there is no spiral cochlea. The alimentary canal and renal and 

 sexual ducts open into a common cloaca, and the primitive urinary 

 organs persist. Respiration, though serial, is not effected by a 

 diaphragm, but the lungs open into the alimentary canal by a short 

 tube, at the anterior end of which is a simple larynx. 



§ 13. Bearing in mind the conditions presented by the other forms 

 of the class Batrachia, we may say that the cat, as a mammal, differs 

 from all Batraciiians, as follows : — 



(1) Its skull has a large parasphenoid, but no presphcnoid. 



(2) Its mandible consists of two bones only, one on each side. 



(3) Its mandible directly articulates with the skull, and there is 



no suspensorium. 



(4) Its auditory ossicles are minute, and take no share in sus- 



pending the mandible of the skull. 



(5) Its ribs join a sternum. 



(6) Its body is furnished with hair. 



(7) Its cerebral hemispheres are large and united by a corpus 



callosum. 



