DISSECTION OF THE SHARK 29 



Fig. 731). Now snip through the sclera near the equator 

 being careful not to injure the dark chorioid tunic. Then 

 put the specimen into water and; separating the sclera and 

 chorioidea, remove the former, at least in part. Brushing 

 away the pigment will serve to demonstrate the venae vorti- 

 cosse. Look for the ciliary nerves. Identify the region of 

 the ciliary body and, cutting away the cornea, expose the 

 iris. 



The anterior and posterior hemispheres may now be 

 separated by cutting through the chorioidea and retina and 

 loosening the corpus vitreum from the ciliary region. Study 

 the anterior segment with a hand lense and identify: retina, 

 ora serrata, orbicularis ciliaris, processus ciliaris and iris. 

 By an incision into the capsule of the lens remove the latter 

 and note its shape and consistency. See: Cunningham ('15), 

 Fig. 686; Morris ('14), Fig. 801; Sobotta ('11), Figs. 733-736; 

 Spalteholz ('09), Fig. 840. In the posterior segment identify 

 the papilla optica (blind spot) and retinal vessels. When the 

 retina is stripped off, the pigment layer usually remains 

 adherent to the chorioid. It is partly replaced in the ox by 

 the iridescent tapetum. 



If microscopic sections are available study the structure 

 about the iridial angle and the layers of the retina. For 

 details of structure of the retina see Section 135. 



15. Cranial Nerves. 'There are ten pairs of cranial nerves 

 (the XI and XII human nerves are not separately represented) . 

 The spinal nerves are much alike, each pair repeating the same 

 functional pattern; but no two cranial nerves have the same 

 functional composition. Accordingly, in studying the cranial 

 nerves it is necessary to determine for each pair of nerves the 

 functional composition of each of its roots and the precise periph- 

 eral and central connections of the fibers of each functionally 

 distinct root. This has been done for a sufficient number of 

 vertebrate types to establish a typical vertebrate pattern of 

 cranial nerve components. These functionally defined com- 

 ponents are classified in four major groups, somatic sensory and 

 motor and visceral sensory and motor, each of which may be 

 further subdivided. For the discussion of the principles and 

 mode of application of this classification (which is fundamental 



