CHAPTER VII 



NERVOUS SYSTEM— SENSE ORGANS 



THE brain is small and of very oblong shape. It 

 consists of smooth cerebral hemispheres, small 

 optic lobes, a still smaller cerebellum, and long olfac- 

 tory lobes ; the pineal body is not accompanied by a 

 parietal organ. The spinal accessory cranial nerve 

 is absent, and the sympathetic system is but feebly 

 developed. 



The eyes have been noticed above (p. 12). When 

 normally developed they are susceptible of a slight 

 movement under the transparent disc, quite indepen- 

 dent from the cornea, which covers them, and from 

 which they are separated by the so-called " lacrymal 

 chamber." There are two lacrymal glands, one in 

 front and one behind ; the lacrymal duct opens into 

 the posterior nares. A sclerotic bony ring is absent. 



The olfactory organ proper is little developed, but 

 is accompanied by an accessory organ, Jacobson's 

 organ, consisting of a pair of pediculate, cup-shaped 

 sacs, between the nasal sacs and the roof of the 

 mouth, encapsuled by the vomers and the turbinal 

 bones, lined by olfactory epithelium, and opening in 

 the mouth just in front of the choanae. As this 



73 



