458 TEE CAT. [CHAP. xm. 



The brain has very small cerebral hemispheres unconnected by 

 any corpus callosum, and the optic lobes are relatively very large, 

 thus agreeing with the brain of the embryonic cat. There are 

 no hypoglossal nerves, and the olfactory nerves do not traverse 

 any cribriform plate, nor has the ear any tympanic membrane, spiral 

 cochlea or fenestra ovalis. There are no Fallopian tubes, and the 

 ovaries in the female are (as well as the testes in the male) directly 

 continuous with ducts which lead to the exterior. There is no cloaca 

 and there is no penis, but the anal, urinary, and sexual apertures all 

 open on the surface of the body, the anal opening being in front and 

 the urinary opening the most posteriorly situated. No temporary 

 urinary organs are developed to be replaced by true kidneys, but the 

 primitive urinary organs persist. The blood is cold, and its red cor- 

 puscles are nucleated. There being no lungs and no trachea, there 

 is of course no larynx. Similarly there is no diaphragm, such as 

 we have met with in the cat. 



Fishes, generally, agree with the cod in the above-mentioned 

 characters, but some exceptions should be noted. The lowly orga- 

 nization of the lancelet has been already referred to. Amongst the 

 highest fishes, such as the sharks and rays, the skeleton is cartila- 

 ginous ; there is a cloaca, and there are Fallopian tubes. In the 

 very exceptional mud-fish (Lepidosiren) the heart has two auricles, 

 the nostrils open posteriorly within the front of the mouth, and 

 there are lungs and a pulmonic circulation. 



11. The cat then, inasmuch as it is a MAMMAL, may be said to 

 differ from the class of FISHES in the following points : 



(1) It has a skeleton, the appendicular parts of which have the 



typical differentiation. 



(2) The hyoid is a structure with simple thyro-hyals, which are 



not in the form of successive arches. 



(3) The skull has a large basi-sphenoid, without any para- 



sphenoid. 



(4) It has a petrous bone. 



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



(6) The mandible directly articulates with the skull, and there 



is no suspensorium. 



(7) The auditory ossicles are minute, and take no share in sus- 



pending the mandibles to the skull. 



(8) There are cervical vertebrae. 



(9) Its ribs join a sternum. 



(10) Having pelvic limbs,* its pelvis is united dorsally to a 



sacrum. 



(11) The body is furnished with hair. 



(12) The muscles of its limbs are complex.! 



* This expression is adopted because 

 in some mammals which have no pelvic 

 limbs there is no junction of pelvis and 



sacrum. | those of the cod. 



j* Even in mammals such as the por- 

 poise, in which the limbs are mere pad- 

 dles, the muscles are very different from 



