ON THE GREENLAND RIGHT-WHALE. 93 



well as in the opposite surface of the cranium, we find them in the newborn specimen still only 

 in the form of short or irregularly triangular pieces of bone t'), in which only by the lateral 

 position and the junction with the zygomatic [s) can we recognise those bony masses which in 

 the full-grown animal are developed to such an extraordinary degree, especially behind and 

 outwardly, as well as greatly removed in a backward direction. 



The petrous bone in the newborn specimen is also of a much simpler form than in the 

 full-grown one, where (ic) it is exceedingly hard and rough. The junction between it and the 

 tympanic is, as usual in the Cetaceans, effected by means of thin, but solid, osseous prolongations, 

 one of which is the processus anterior mallei ; these are very easily broken. The petrous bone 

 itself, on the contrary, is exceedingly firmly wedged in between the remaining bones of the skull, 

 especially by means of the two osseous processes already described and figured by Cuvier. 

 We have represented this very complicated junction of the petrous bone with the adjoining 

 bones in Plate V, fig. 4, as it appears on the left side of the head when looked at from 

 below and from the front. 



In this figure (four and a half times diminished) the letters have the following significations : 



a. The tympanic {bulla tympani). 



b. The petrous bone. 



b'. The thin and sharp plate of this bone, forming the anterior wall of the inner- 

 most part of the auditory meatus in which the sack-Hke eversion of the 

 membrana tympani is placed. 



c. The foremost and (towards o') lower surface of the external tenon-like process of 



the petrous bone, of which the former, together with x, forms the hindmost 

 wall of the auditory meatus. 



d. The internal process of the petrous bone, as far as it is firm and osseous. 



éT. The internal process of the petrous bone, as far as it consists of a spongy 

 mass. 



e (and h). The portion of the occipital entering into the inner wall of the pterygoid 

 cavity. 



/. The roof of the pterygoid cavity, formed by the occipital. 



g. The portion of the pterygoid entering into the internal wall of the pterygoid cavity. 



h (and e). The portion of the occipital entering into the internal wall of the 

 pterygoid cavity. 



0. The occipital. 



o'. The inferior rough surface of the lateral portion of the occipital joining the 

 lowest surface of the external tenon-like process of the petrous bone. 



p. The pterygoid. 



t. The temporal. 



i. The inner wall of the articular portion of the temporal. 



f. A spongy prolongation of the temporal joining d°. 



x. The posterior wall of the auditory meatus as far as it is formed by the temporal. 



y. Interval between the petrous bone and the lower surface of the articular 

 portion of the temporal, filled with a strong fibrous tissue for the attach- 

 ment of the petrous bone. 



z. The entrance of the pterygoid cavity. 



