8o ANATOMY OF A CHELONIAN. 



the other [descendens noni) arises from the hypoglossal, 

 close to its foramen of exit, and runs back among the 

 muscles of the neck. 



203. Repeat on the other side the dissections given 

 in sections 196-202, inclusive, and then, with a pair 

 of bone forceps break away the base of the skull in 

 the middle line, so as to expose the ventral aspect of 

 the medulla oblongata ; with care this can be done 

 without injuring the nerves above described, which are 

 then to be followed into the cranial cavity, bits of bone 

 being broken away as may be necessary, with strong 

 scissors or a stout needle mounted on a handle. The 

 hypoglossal may thus be followed to its superficial 

 origin (180, /); the pneumogastric, spinal accessory, and 

 glosso-pharyngeal traced from the superior cervical 

 ganglion to the brain ; and the seventh nerve followed 

 through the bone in front of the auditory capsule to the 

 cranial cavity. Then remove the eyeballs, and cut off 

 the head and the upper part of the neck and place 

 aside in strong alcohol to harden the brain. 



204. To study the Anatomy of the Eyeball, clean away 

 the muscles, etc., from its exterior. Note: 



a. The transparent cornea in front, forming a seg- 

 ment of a smaller sphere than the semi-opaque 

 sclerotic behind, which has a bluish tint from 

 the choroidal pigment seen through it. In the 

 anterior part of the sclerotic bony plates may 

 be felt imbedded in it, forming a ring just where 

 it meets the cornea. The conjunctiva on the 

 front of sclerotic contains much dark pigment. 



b. Cut away the cornea ; note the anterior chain- 



