394 E. A. BAUMGARTNER 
connection with the mouth is soon lost and in a 90 mm. stage 
the whole structure has come into closer relation with the brain 
floor and vascular sac, and has grown forward. ‘The roof of the 
hypophysis has become thickened, as have the anterior and 
posterior ends. From the floor of the caudal end two lateral 
outpouchings have developed which later form the inferior sacs. 
In a 20 cm. Mustelus all parts of the hypophysis are quite well 
developed. A vascular layer separates the roof from the brain 
floor. The roof of the inferior sacs becomes thinner. Haller 
also described the interhypophyseal canal joining the inferior 
sacs to the superior part. He figured glandular outgrowths 
extending forward from it. From the floor of the anterior 
sac are several prolongations extending anteriorly while from the 
roof are many small outpouchings. The extreme anterior end 
shows many mitotic figures and is broken up into a network 
by many capillaries. The floor at the cephalic end of the ante- 
_rior lobe is very thin—this, Haller stated, is where the hypophysis ° 
is constricted from the mouth and here the epithelium has re- 
mained of a low cuboidal type. The head of the organ is com- 
posed of many closely-crowded tubules. These develop first as 
solid evaginations, then the nuclei separate and rearrange them- 
selves, later a cleft appears in the protoplasm, which cleft ulti- 
mately connects with the main lumen. 
Chiarugi (’98) briefly considered the hypophysis in a paper on 
the description of a’ prehypophyseal body and the hypophyseal 
area in Torpedo ocellata. He described a connection between 
the premandibular somites and the hypophysis and figured a 
median sagittal section of a 15 mm. embryo which showed a 
constriction of the hypophysis from the mouth. 
Nishikawa (’99) noted that the hypophysis is present as a 
simple outpouching in 32 mm, Chlamydoselachus embryos. 
He made a series of drawings of transverse sections which show 
its position at this stage.- 
Sewertzoff (99) in studying the development of the selachian 
skull took up the interrelation of development of the skull and 
brain. The trabeculae and parachordal plates in Acanthias 
and Pristiurus are almost at right angles to each other in early 
