476 SCHULTE, SEI WHALE. 



and narrow. It is inserted between the tuberosity of the maxilla and the internal pterygoid. 

 Between its summit and the presphenoid is a moderate sphenopalatine foramen. 



The internal pterygoid appears on the base between the palate and the external pterygoid, 

 sending a narrow process dorsad which joins and underlies a descending process of the frontal. 

 The hamular processes are very large, curving ventrad and mesad and overhanging the audi- 

 tory bulla. The exposed surface of the external pterygoid is interposed between the squamosal 

 and internal pterygoid, and lies in the same plane as these bones, with which it is suturally 

 united. From its junction with the latter arises the m. pterygoideus externus, the internus 

 taking origin from the internal pterygoid and that margin of the palate bone which articulates 

 with it. There is thus no pterygoid fossa. 



From the basisphenoid the small triangular processus alaris projects laterad nearly at the 

 level of the dorsal surface of the sella turcica. This is still wholly cartilaginous. It is continued 

 laterad by the processus ascendens alae temporalis, in which ossification has begun. The latter 

 process is cylindrical, slightly expanded at its extremity, which ascends and conies to the surface 

 in the temporal fossa in the interval between the parietal, squamosal and external pterygoid. 

 In the adult Balcenoptera a bone presenting in this position has been taken by Carte and Mac- 

 Alister 1 for basisphenoid, and Dwight 2 concurs in this usage, remarking that he does so "from 

 information derived from the works of other observers, for it would be impossible to name it 

 from the little that is seen on the unopened skull." He states that in B. musculus it lies between 

 the parietal and the alisphenoid; in B. rostrata (= acuto-rostrata) , he quotes Carte and Mac- 

 Alister as finding it in contact also with the squamosal. As a matter of literal fact they say 

 mastoid, but as this is inconceivable, I prefer with Dwight to take their meaning to be squa- 

 mosal. As this region of the skull is highly specialized and in the adult many of the sutures 

 are obliterated, it is not surprising that attempts at its analysis on the basis of adult material 

 alone should have been largely erroneous. The matter is much simpler in the light of deBurlet's 3 

 fine studies of the chondrocranium in Cetacea, which have revealed the small size and cylindrical 

 form of the ala temporalis. In his reconstruction of B. rostrata ( = acuto-rostrata) this process, 

 which corresponds in shape and position closely with that of this foetus, projects freely into the 

 wide fenestra sphenoparietalis, its extremity approaching close to the orbitoparietal commissure. 

 It is therefore evident, that, when the fenestra is closed by the development of membrane bones, 

 their margins will come in contact with the ala temporalis, the extremity of which will appear 

 in the definitive temporal fossa as is usual in mammals, the peculiarity of the Cetacean skull 

 consisting merely in the small size of the ala temporalis (alisphenoid) . 



If, then, the basisphenoid of the authors quoted becomes ala temporalis, a reinterpretation 

 is necessary of the ventrally placed element, which they take for alisphenoid. This I have 

 already described as external pterygoid. Carte and MacAlister, to be sure, term it alisphenoid 

 or pterygoid bone, but then state that ventrally it divides into two pterygoid plates, which 

 include between them a large ovoid pterygoid fossa. I have already expressed the opinion 

 that the pterygoid fossa is absent in this skull, from which it follows that the fossa here in ques- 

 tion must receive another interpretation. I take it to be the scaphoid fossa. To substantiate 



1 Carte and MacAlister, op. cit., p. 208. 



2 Dwight, T. Description of the whale (Balaenoptera musculus Auct.) in the possession of the Society, with remarks on the classi- 

 fication of fin whales. Mem. Boston Soc. Nat. Hist., 1871, Vol. 11, p. 208. 



MeBurlet, H. M. Zur Entwicklungsgeschichte des Walschadels, III. Das Primordialcranium eines Embryo von Balamoptera 

 rostrata (105 mm.). Morph. Jahrb., Bd. 49, 1914, p. 119. Cf. also I. and II., Morph. Jahrb., Bd. 45 and Bd. 47, p. 644. Phocama 

 communis; and IV. Morph. Jahrb., Bd. 49, p. 393. Lagenorhynchus albirostris. 



