312 Susanna Phelps Gage 



Fig. 85. Shows the origin of the 6th nerve caudad of the 8th, and 

 what is rare at tliis stage of growth, several capillaries entering the 

 brain close together. 



Fig. 86. Through the lotli nerve and ganglion and a part of the sul- 

 cus from which the 9th nerve passes off. 



Fig. 87. Shows the 1 itli nerve and jc a bundle of fibers which can be 

 traced for some distance in the medulla. 



Fig. 88. Shows the origin of the 12th nerve. 



Fig. 89. Shows the beginning of the myel and a nerve root. 



Fig. 90. An enlargement of the dorsal part of Fig. 80. Shows the 

 epiphysis and the dorsal enlargement of the diacoele ventrad of it. X 

 150. 



Fig. 91. An enlarged section between Fig. 78 and 80, to show the 

 supracommissure, the rudiment of the callosuni, the opening of the 

 paraphysis ventrad of the diaplexus. X 150. 



Fig. 92. An enlargement of the lateral part of Fig. 84, to show the 

 origin of the 7th and 8tU nerves, and part of their ganglia, the 7th is 

 continuous at its dorsal part, with cells of cinerea which form a " Rau- 

 tenlippe " or sulcus. A blood vessel extends among the fibers of both 

 the 7th and 8th. X 150. 



PLATE VIII. 



Mesal view of the brain of a small Ajnia calva, reconstructed 

 from transections, of which Fig. 94-100 are a few. X about 6J-2. Mesal 

 views by Goronowitsch (21), of Acipenser ruthenus, by Herrick (24), 

 and Wilder (50), of lepidosteus differ somewhat from this though there 

 is a general agreement. The pia is shown as extending from the auli- 

 plexus between the olfactory lobes, and on the dorsal part of the gemi- 

 nums. It is not shown on the ventral side at all. The opening into 

 the rhinoccele is not called a porta. No union except the terma between 

 the hemicerebrums occurs until the commissure cm. From the infun- 

 dibulum a cavity extends cephalad (Fig. 98), and four caudad I Fig. 100). 

 The paraphysis and epiphysis open into the cavities (Fig. 98-99) and 

 the latter at the usual place between supra- and postcommissures. The 

 geminums unite by a commissure which is depressed below the dorsal 

 limit (Fig. 100), and form a caudal recess over the valvula. The 

 metaplexus extends as a pocket over the cephalic end of the myel, z, 

 in a region comparable to the metapore. At x the dorsal walls of the 

 medulla nearly meet. The endymal surface is shown marked b}- sulci. 



Fig. 94-100. Transections of same. X about lYz. The endyma is 

 represented by a chain of cells, the cinerea by dots ; the larger blood 

 vessels penetrating the brain are shown. 



Fig. 94. At the right the rhinoccele is completelj^ circumscribed, at 

 the left is just closed off from the sulcus re of Fig. 95. The pallium ex- 

 tends to the extreme lateral border and by a fold on the meson forms 

 two paracoeles. 



Fig. 95. The mesal fold of F'ig. 94 is separated into the auliplexus 

 and crista. 



Fig. 96. An enlargement of the crista of Fig. 95. X 22. There is no 

 enlargement of the brain at this point except by endyma. The fibers 

 in the crista are like those in the membranes. 



Fig. 97. Shows the union of hemicerebrums by the commissure cm. 

 At the left are indicated the capillaries which extend as a network 

 throughout the brain substance to the endyma. Contrast Fig. loi. At 



