SCHULTE, SEI WHALE. 481 



obliquely directed, rising rostrad and making an angle of about 30 with the long axis of the 

 head. With the dura in place the cavity is smooth walled, the irregularities between the bones 

 being filled with dense connective tissue; especially is this the case around the otic capsule. The 

 falx cerebri is narrow, beginning upon the mesethmoid which has a low median ridge for its 

 attachment, and extending to the supra-occipital where it meets the tentorium. Beyond this 

 the falx cerebelli is represented by a minimal median fold. The tentorium is broader than the 

 falx; it rises steeply, its plane making an angle of about 70 with the basis cranii. Its aperture 

 is elongated dorso-ventrally, contracted from side to side. Ventrad its margin broadens to its 

 attachment to the rudimentary dorsum sellse and the side of the shallow sella turcica. A second 

 low fold of dura extends from the dorsal margin of the foramen magnum obliquely ventrad and 

 rostrad, terminating in an arch which surrounds the porus acousticus internus on its dorsal and 

 rostral contours. Beneath the middle third of this fold is the jugular foramen, divided by dura 

 into a rostral compartment for the hypoglossal, this subdivided into two parts, for the nerve 

 pierces the dura in two divisions, and a caudal one for the glossopharyngeal and vago-accessorius. 

 The facial and acoustic nerves as noted above pass out beneath its extremity, while the fifth 

 has a large dural foramen midway between this fold and the tentorium. For the rest, the 

 posterior fossa offers little to comment upon; its floor is concave and rises caudad to the fora- 

 men magnum, so that the region of the clivus does not form a continuous ascent. 



The middle and anterior cerebral fossae are but very imperfectly demarcated on the floor, 

 owing to the lack of prominence of the ala orbitalis. This however is recognizable and the 

 distance from its caudad margin to the rostral pole of the cavity exceeds that from the same point 

 to the tentorium. The anterior fossa appears therefore enlarged at the expense of the middle. 

 The sella turcica is shallow but broad, and the cavity in the dura which lodges the hypophysis 

 has corresponding proportions. The diaphragma sellse is narrow and zonular with a large fora- 

 men. The optic nerve enters the dura at the side of the olivary eminence and has a long sub- 

 dural course before reaching the optic foramen. The cribriform area is depressed and a sharp 

 lateral and rostral margin defines it from the frontal and from the lateral ethmoid. In it are 

 three small foramina for olfactory nerves. 



After the removal of the dura the conditions of the cranial elements, apart from the appear- 

 ance of ossification centres and of membrane bones, was found to correspond very closely to 

 the pattern of the chondrocranium of B. acuto-rostrata of 105 mm., modelled and described by 

 deBurlet. There are a few changes however, the taenia metoptica has been partially absorbed 

 so that the optic foramen is now confluent with the sphenoidal fissure, but otherwise the fenes- 

 tra spheno-parietalis has much the same shape and relative size as in deBurlet's model. The 

 commissura orbito-parietalis persists as a narrow and thin bar of cartilage at its dorso-lateral 

 margin, now overlain ectally by the parietal bone. Caudally the commissura expands moder- 

 ately and joins the otic capsule at the origin of the commissura prsefacialis, but here stops with- 

 out reaching the occipital, so that the lamina parietalis seems largely to have been absorbed. 

 In consequence there is in this region a small lateral fontanelle between exoccipital, parietal 

 and otic capsule; in the angle between the two latter a small triangle of squamosal appears, 

 which in the natural condition is covered by fibrous tissue excluding it from the cranial cavity. 



The fenestra spheno-parietalis is partially subdivided by the rod-shaped ala temporalis. 

 This as in deBurlet's model falls short of reaching the commissura orbito-parietalis by a narrow 

 interval. The extremity of the ala temporalis appears in the temporal fossa, as has been noted 



