408 E. A. BAUMGARTNER 
anterior part of the hypophyseal evagination is growing between 
the brain and the median mass connecting the premandibular 
somites, the posterior portion forms a more or less prominent 
ridge caudal to the connecting mass of the somites. A model 
of such an embryo shows as an evagination, the end of which is 
grooved transversely by the median mass connecting the pre- 
mandibular somites (fig. 2). This groove may be quite promi- 
nent even in 11 to 12 mm. embryos and evidences of it are 
usually to be found at that time. 
In 8 mm. embryos as well as in younger ones the anterior arm 
of the hypophyseal outpouching shows differentiation as far 
forward as the postoptic recess (fig. 2). Scammon (’11) stated 
that the notochord comes into contact with the early hypo- 
physeal outpouching, and Sterzi (712) has shown such a contact 
in Mustelus of 8 mm. (fig. 449). No such contact has been 
observed in this study of Acanthias. 
A mid-sagittal section of a 15 mm. embryo shows that the 
superior end of the hypophysis has now grown well between the 
brain and the median mass connecting the premandibular somites. 
The evagination is more marked and the anterior arm is longer 
than in younger stages (fig. 3). 
A model of the hypophysis of an Acanthias embryo 19 mm. in 
length is shown in figure 11; this view is taken from the left 
lateral side. The hypophysis at this stage is an anteriorly and 
dorsally directed outpouching, concave on its ventral surface 
where it lies in close relation to the diencephalon (fig. 18). Its 
superior anterior end extends to the infundibular recess. The 
opening from the pharynx into the hypophysis is small. A 
sagittal section at about the median line (fig. 4) shows that the 
thickened anterior (ventral) wall of the hypophysis extends 
forward as far as the postoptic groove as Johnston (09) has 
figured it. 
Fig. 11 Left lateral view of a reconstruction of the hypophysis of a 19 mm. 
embryo. .X< 130. Mo, lining of mouth; H, hypophysis. 
Fig. 12 Left lateral view of a reconstruction of the hypophysis of a 21 mm. 
embryo. X 100. a, anlage of anterior end of hypophysis; H, hypophysis; IL, 
anlage of the inferior lobes; Mo, lining of mouth. 
