482 SCHULTE, SEI WHALE. 



in the account of the exterior of the skull, between the external pterygoid and the parietal. 

 Mesad it is suturally attached to a process of the basisphenoid (processus alaris) which completes 

 the boundary of the sphenoidal fissure caudad. Owing to the interval which exists between the 

 lateral extremities of the ala temporalis and ala orbitalis a small segment of parietal closes the 

 fissure at this point. The sphenoidal fissure is confluent with the optic foramen, but not broadly 

 for a remnant of the ta3nis metoptica persists as a process of the ala orbitalis. In addition to 

 its usual contents it transmits the maxillary division of the quintus, there being no foramen 

 rotundum. Caudal to it is the foramen ovale at the bottom of the triangular interval between 

 it and the otic capsule. This space is largely filled with fibrous tissue, upon the removal of 

 which the ventral angle of the parietal and a small area of squamosal are seen closing the space 

 lateral and dorsal to the foramen ovale. 



The otic capsule has advanced little beyond the condition recorded by deBurlet. The fissura 

 basi-capsularis is marked by a deep groove, in the caudal part of which is situated the jugular 

 foramen, and more mesally but close to it the foramen perilymphaticus still confluent with the 

 fenestra rotunda. Rostrad toward the dorsum sellao there is a very broad basi-cochlear com- 

 missure of cartilage and here the surface of the otic capsule slopes into that of the basisphencid 

 without visible demarcation. The ental orifice of the carotid canal is situated as in deBurlet's 

 model at the caudal margin of the processus alaris with the alse-cochlear commissure forming 

 its lateral boundary. The canal begins ventrad, at the caudal margin of the internal pterygoid 

 plate and is directed rostrad, dorsad and laterad through the basisphenoid. It is of small di- 

 mensions as the carotid artery is smaller than the vertebral in this foetus. The line of attach- 

 ment of the tentorium to the otic capsule is indicated by a low ridge which terminates between 

 the foramen perilymphaticus and the porus acousticus internus. The latter is narrowed by a 

 zonular fold of dura, but in the cartilage gapes widely and is divided by a ridge of cartilage into 

 a dorsal and a ventral portion. The canalis facialis is hardly more roofed in than in deBurlet's 

 foetus and the commissura prafacialis is not proportionately increased in size. The ridge for 

 the tentorium becomes grooved in its dorsal portion and in this groove appears the foramen 

 endolymphaticus. 



The ental surface of the basi-occipital descends from the foramen magnum and again rises 

 towards its junction with the basisphenoid. Its ossification centre, which presents ectally as a 

 narrow strip, expands towards the cerebral cavity and on its ental surface occupies the whole 

 breadth of the cartilage. It is separated from the spherical ossification centre of the basisphenoid 

 by a wide mass of cartilage which dorsally projects as a low ridge into the cranial cavity. Ros- 

 trad of this there is a concavity which lodges the hypophysis. The ridge must therefore be the 

 dorsum sellse, the concavity the sella turcica. This in turn is limited rostrad by a second low 

 transverse ridge, the olivary eminence, which laterally terminates in a small conical projection, 

 the remains of the tsenia postoptica. Rostrad of this again is a shallow concavity, the cerebral 

 surface of the presphenoid, in which have appeared a pair of small ossification centres, which 

 have not yet united in the midline. The ala orbitalis is very large and terminates on the ental 

 surface of the frontal with a concave margin. The tsenia prooptica is broad and convex dorsad 

 where it forms the boundary of the orbito-nasal foramen which gives passage to the large nasal 

 nerve. Elsewhere the orbito-nasal fissure is reduced to linear dimensions and closed by mem- 

 brane. 



The large and wide area between the presphenoid and the frontal is occupied by the cere- 



