158 PROFESSOR STRUTHERS. 



culus, may in part account for the differences in the nasal bones, 

 especially for their lateral compression behind in Megaptera. 



9. LENGTH AND PROPORTIONS OF THE CRANIUM. The length 

 of the cranium, from the back of the occipital condyles, may be 

 taken to several points. If to the anterior end of the nasals, it is 

 influenced by the very variable nasal bones ; if to the anterior 

 end of the temporal fossa, it is influenced by the muscular 

 arrangements. To the posterior end of the nasal bones is prob- 

 ably the best point. These three measurements are given in 

 the table (Table I. Nos. 45, 46, and 47). Taken at the latter 

 point the length of the cranium is only J inch more in B. 

 musculus than in Megaptera (32J and 32), while in total length 

 the skull in the B. musculus exceeds that of Megaptera by 20 

 inches (145 and 125). In breadth the cranium of Megaptera 

 exceeds that of B. musculus considerably, at the greatest breadth 

 (measurement No. 15) by 4 to 5 inches (71J and 66J). The 

 greatest length and greatest breadth of the skull are, respec- 

 tively in inches, in Megaptera 125 and 71J, in the B. musculus 

 145 and 66 J. 



10. NASAL BONES. The nasal bones are very different in Me- 

 gaptera and B. musculus. 1 The typical form of the nasals in fin- 

 whales is that which the human nasals would present were they 

 thickened towards the nasal cavity until the thickness exceeded 

 the breadth. What would have formed the sixth surface of 

 a four-sided block is reduced to a border by the sloping of 

 the superficial and inferior surfaces to an anterior free border. 

 Differences are seen in the amount of transverse concavity and 

 compression of the superficial surface, in the concavity of the 

 free border, in the separation of the inner borders by a trough-like 



1 -Professor Flower has given (Proc. Zool. Soc., 1864, p. 390) an interesting 

 series of drawings of the superficial surface of the nasal bones. It is not easy to 

 give by one view a satisfactory idea of the form of these bones, to show especially 

 their 'variously grooved condition. The nasals of this Megaptera differ from his 

 figure (fig. 3) in that their outer margin, at the anterior end, falls short of the 

 inner margin at the peak by only 1 inch (about ^ of the whole inner border), and 

 that the triangular space between the nasals runs all the way, tapering to the 

 peak where the two nasals come clcfse together. Compared with his figure (fig. 4) 

 of B. musculus, the outer margins in this B. musculus go much farther forwards, 

 the inner margins form a prominent narrow mesial peak, and at the posterior 

 border the obliquity is in the opposite direction, viz., forwards and outwards, at 

 an angle of 45. 



