ART. 15. A NEW GENUS OF WHALE FROM MARYLAND KELLOGG. 11 



opening of the facial canal, which pierces the pro-otic as men- 

 tioned above and then turns obliquely backward at the point where it 

 enters the labyrinthic. Thus the pro-otic and labyrinthic portions 

 of the facial canal form an acute angle with each other at their 

 junction. 



External to the internal acoustic meatus and anterior to the slit- 

 like depression is a minute opening, which may possibly be the 

 aqueductus vestibuli. Near the posterior margin of the labyrinthic 

 and adjacent to the internal acoustic meatus is the opening of a small 

 canal, which connects with the fenestra rotundum below it. The 

 latter is the external aperture of the aquaeductus cochleae. There 

 is a small concavity on the posterior face of the labyrinthic above 

 the aperture of the aquaeductus cochleae and the internal acoustic 

 meatus. 



MEASUREMENTS OF THB PERIOTIC BONE. 



Greatest length of periotic (tip of anterior process to tip of posterior mm. 



process) 82 



Greatest deptli of labyrinthic region of periotic 15.7 



Greatest breadth of labyrinthic region of periotic 29.5 



Length of posterior process or apophysis (external wall of groove for 



facial canal to tip of apophysis) 47 



Greatest antero-posterior diameter of apophysis 26 



Distance from apex of labyrinthic to tip of the process below foramen 



rotundum that projects backward and inward 30. 7 



TYMPANIC. 



Perfect conjoined tympanic and periotic bones have not as 3 et been 

 found in the Calvert Cliffs'. Since the periotic and the tympanic 

 bones of the Cetacea are joined together by two small processes they 

 would hardly escape .being broken apart while the skull was being 

 rolled about by the water. In most of the Mystacoceti the periotic 

 is firmly lodged and is held in place by the apophysis and the project- 

 ing edges of the squamosal bone. Hence the periotic is usually in 

 place when the skull is excavated. In exceptional cases the tympanic 

 bone is not dislodged by the action of the water, but in such cases 

 the weight or pressure of the overlying beds breaks the connections 

 and crushes the fragile processes which project from the tympanic. 

 As a result of these destructive forces practically all of the tympanies 

 found are fractured or broken. 



The single tympanic bone (pi. 6, fig. \h) which was found asso- 

 ciated with the skull is imperfect ; part of the thin outer lip, as well 

 IS the anterior process and the accessory ossicle borne by it, are 

 missing. It was found that the fractured end of the posterior process 

 of the tympanic fits into the corresponding surface of the fragment 

 of this process that is ankylosed to the apophysis of the left periotic. 

 The contact between the proximal and distal fragments of the poste- 

 rior process is sufficiently close to justify the association of this 

 tympanic with the left periotic. 



