18 



into the posterior side of the sacculus. During life the utrici 

 sacculus and the semicircular canals are filled with a lymph 

 fluid, and the sacculus contains a large calcerous ear-stone (otolii 

 which is usually dissolved by the formalin used in preserving 

 dogfish. 



Whitish patches of thickened sensory epithelium may be seei 

 the ampullae (cristate acusticae) and in the utriculo-saccular ch 

 her (maculae acusticae). Branches of the eighth nerve can be 

 lowed to all these areas. 



A projection of the ventral wall of the utriculo-sacculus is 

 lagena, the rudiment from which the cochlea of higher anin 

 developed. It also contains a macula acustica. 



EXTERNAL FEATURES OF THE EYE. Observe the transpa: 

 cornea covering the external surface of the eye; the dark ring 

 the iris; the central opening in the iris, the pupil; the conjur 

 val sac surrounding the external half of the eyeball. Cut a 

 sufficient of the upper wall of the cartilaginous orbit to expose 

 eyeball and its muscles. Note the considerable amount of soft < 

 nective tissue around the eye and explore the orbital sinus (p. ] 

 Take notice of the following nerves, in order to ensure their pre 

 vation until the time comes to trace them more completely. A h 

 nerve crossing the medial side of the orbit, the superficial opht 

 mic; a nerve leaving the cranium opposite the optic lobe, pas: 

 under the superficial ophthalmic to the anterior muscle of the 

 ball, the trochlear; several long ciliary nerves passing to the 

 ball; several other nerves visible in the deep angle of the orbit. 



Six muscles move the eye. Four of these arise close toge 

 at the deep postero-medial angle of the orbit. Diverging, they 

 inserted upon four sides of the eyeball, and from the positior 

 their insertions are named the superior, posterior, inferior, 

 anterior recti. Two muscles arise from the antero-medial angl< 

 the orbit, the superior and inferior oblique muscles. 



Between the recti muscles can be seen a mushroom-shaped s 

 of cartilage, the ophthalmic peduncle; the eyeball rests againsi 

 expanded end. (There is no peduncle in Eugaleus.) 



THE CRANIAL NERVES. The cranial nerves are twelve pair; 

 nerves arising from the brain, and thus distinguished from the sp 

 nerves which arise from the sides of the spinal cord. They are 

 tributed chiefly to the head and neck, though branches of the vi 

 nerve go to the viscera and to the sense organs of the lateral ] 

 Since the nerves are all paired, the distribution of both nerves < 

 pair being alike, the descriptions will mention but one nerve < 

 pair. As the cranial nerves are traced dissect away the sides of 

 cranium down to the foramina penetrated by the nerves, and fol 

 each nerve from its origin on the brain to the parts innervated b 

 Features of the dissection which are not found in tracing the n< 

 of one side should be sought on the other side. 



The olfactory nerve. The anterior surface of the olfactory 1 

 fills a large foramen in the anterior wall of the cranium am 

 pressed closely against the posterior surface of the nasal sac. 

 merous small nerves, collectively forming the olfactory nerve, a 

 from the anterior face of the lobe, penetrate the membraneous i 

 of the olfactory organ, and are distributed to its highly folded 

 face. 



The terminal nerve, Nervus terminalis, is a slender nerve : 

 ning along the medial surface of the stalk of the olfactory 1< 

 Follow it backward to its origin on the anterior surface of the c 



