ANATOMY OF MEGAPTERA LONGIMANA. 151 



upper border, going outwards, slopes in Megaptera a little 

 downwards, in B. musculus very much upwards. The more 

 square form in Megaptera is mainly owing to the greater height 

 at the inner part, from the temporal fossa cutting less back 

 into it, and to the greater general breadth. 



4. TEMPORAL FOSSA AND PASSAGE. When these skulls are 

 viewed anatomically, from above as well as from the side, it is 

 seen that the parts connected with the temporal muscle present 

 the most marked of all the characters which differentiate the 

 skull of Megaptera. Considering the enormous length of the 

 mandible in whalebone whales, and its weight even in the 

 water, we would expect to find a correspondingly large temporal 

 fossa and passage, and, as the head is flat, that the fossa would 

 assume an expanded form. 



From the measurements given in the table, it is seen that 

 the temporal fossa is broader by 3 inches in the Megaptera, 

 and longer by 8 inches in B. musculus, and is of nearly the 

 same depth in each, at the deepest part, which is towards the 

 back part of the inner side. From 5 to 6 inches of the greater 

 length in B. musculus is obtained by an angular prolongation 

 behind where the zygoma and squame of the temporal meet, 

 while in Megaptera the posterior border is uniformly concave. 

 The great difference, however, is in the shortness of the fossa at 

 its outer compared with its inner part, being in Megaptera 

 scarcely half as long externally as it is internally. This is 

 owing to the well-known obliquity backwards of the orbital 

 process of the maxillary and of the anterior border of the 

 orbital plate of the frontal, so that at the outer part that plate 

 is but 12 inches in length, as compared with 27 inter- 

 nally, two of the 27 covered by the maxillary at the anterior 

 end of the fossa. In B. musculus the obliquity is very much 

 less, the measurements at the corresponding parts . being re- 

 spectively 15J and 29 inches; but about 4 inches of this 

 narrowing is obtained by a forward direction of the posterior 

 border of the plate, while the posterior border of the plate in 

 Megaptera is, on the contrary, directed a little backwards. The 

 less length of the temporal fossa, and its farther back position 

 on the skull, in Megaptera are made manifest by observing its 

 relation to the ends of the maxillary and nasal bones. A line 



