152 PROFESSOR STRUTHERS. 



drawn across the skull where the maxillary and supra-occipital 

 bones come in near relation (the transverse frontal fossa), has 

 in front of it, in Megaptera less than a third of the length of 

 the temporal fossa (9 to 10 inches), only its narrow anterior 

 end, and passes at about 3 to 4 inches in front of the orbit ; 

 while in B. musculus well on to half of the fossa (18 inches) is 

 in front of the line, and it passes across the posterior end of the 

 orbit. In relation to the nasal bones, the anterior boundary of 

 the temporal fossa reaches, in Megaptera to only h inch in 

 front of the median peak of their anterior ends, in B. musculus 

 to 10| inches. A difference is seen also in the level of the 

 floor of the fossa, especially on the outer half of the frontal 

 plate, which in Megaptera is convex with a general fall back- 

 wards (except at the anterior angle), while in B. musculus it is 

 flat with a slight fall forwards. Standing behind the skull, 

 with the eye on a level with the upper border of the occipital 

 plate of the temporal bone, there is seen above it, in B. mus- 

 culus only the inner part of the anterior end of the temporal 

 fossa ; in Megaptera the fossa, with its great slope, is seen in 

 its whole length, and the outer half of the posterior border is 

 also seen. 



The differences in the temporal fossa in Megaptera and B. 

 musculus appear to be mainly owing to the greater breadth of 

 the cranium in Megaptera, in adaptation to a wider mandible 

 requiring the post-mandibular plate of the occipital to be not 

 only farther out but also farther back. 



Tertiporal Passage. — This large aperture, leading down from 

 the back part of the temporal fossa upon the condyle or neck 

 of the mandible, is a continuation of the temporal fossa, but 

 may be conveniently distinguished by the above name. It is 

 large enough to allow a man's body to pass. In Megaptera the 

 posterior wall is uniformly and smoothly concave, with a depth 

 of 10 inches at the middle, and but faintly marked off from 

 the glenoid surface below, both being nearly vertical. In B. 

 musculus there is a well-marked angle in the posterior wall ; 

 the depth at the middle is 7 inches, and the wall here is 

 marked off from the glenoid surface by a strongly pronounced 

 transverse ridge, towards which both surfaces slope forwards. 

 The angle on the posterior wall gives the passage a triangular 



