112 MR, E. PHELPS ALLIS, JUN., ON 



jidult Mvstelus, lying posterior to the foramen olfactorinm and 

 directly above the lobiis olt'actorius. 



The dome-shaped protuberance of Callorhyndnts, the so-called 

 nasal capsule, always lies, at all stages of its development, in the 

 i-egiou between the bases of the median and lateial rostral 

 processes, and as the capsule increases in size the bases of the 

 rostral processes are correspondingly separated from each otlier, 

 and the anterior opening of tlie cranial cavity carried corre- 

 spondingly forward ; but whether this growth of the cranial wall 

 takes place posterior to the fenestra olfactoria of the 60 mm, 

 embryo, or is due to groAvth anterior to that fenestra, cannot be 

 told from the figures. In the one case the nasal sac, which 

 certainly lay primarily anterior and external to the cranijil 

 cavity, would have been pulled relatively backward into the 

 antei-ior end of that cavity; the fenestra olfactoria of the 60 mm. 

 embryo would remain morphologically unchanged, but would 

 change in function fi'om a fenestra olfactoria to a fenestra 

 nasalis ; and the so-called nasal cartilages of Schauinsland's 

 figures would represent detached pieces of an undeveloped nasal 

 capsule. In the other case, the nasal capsule would 1 e developed, 

 as a direct anterior, but morphologically ventral, prolongation of 

 the cranial walls, a fenestra nasalis gradually developing external 

 to the fenestra olfactoria of the 60 mm. embryo. The conditions 

 in the adult Chimm-a decidedly favour this latter view, but one 

 of Schauinsland's figures of Gallorhynchus equally decidedly 

 favours the former view. The figure in question (fig. 165) gives 

 a median vei'tical sectional view of an embryo older than the 

 85 mm. one, and shows the brain in place in the cranial cavity. 

 The trabeculse are shown lying in the line prolonged of the 

 parachoidals, which is not in accord with the figures -of other 

 embryos both older and yoimger than this one. The septal 

 cartilage is shown as a simple rostral stalk, while in the younger, 

 85 mm. embryo, it is already an important plate-like structure 

 the posterior portion of which corresponds to the rostral stalk 

 of the 60 mm. embryo, and the anterior portion to the sub- 

 ethmoidal keel of that stalk. The rostral stalk of the embryo 

 shown in figure 165 projects dorso-posteriorly, instead of, as in 

 the other embryos, dorso-anteriorly, and the ventral portion 

 of the nasal sac is shown extending forwairl anterior to the level 

 of the base of the median rostral process and close to the ventro- 

 anterior corner of the ehondrocranium. The nasal sacs, as hei-e 

 shown, must accordingly project beyond the anterior openings of 

 the cranial cavity, if those openings are found in this embi'yo at 

 all in the positions that they have in the other embryos, both 

 older and younger, and furthermore, they must lie dorsal to the 

 trabeculfe, as they do in Ceratod'us and the Teleostei, instead of 

 ventral to the trabecule, as they do in the Selachii and as they 

 must also in Callorhynchus if the septum nasi of this fish lies 

 ventral to the rostral stalk, as shown in Schauinsland's other 



