410 THE ANATOMY OF VEKTEBEATED ANIMALS. 



after its prey. The point at wliicli the extra bronchus to the 

 right lung is given off is separated by four rings from the 

 bifuj-cation of the trachea. The lungs are not lobed and 

 their tissue is very dense and elastic. 



The cerebral hemispheres are, taken together, broader 

 than they are long. In the upper view they leave not more 

 than a seventh of the length of the cerebellum exposed, while 

 they overlap it largely at the sides. The outer surface of 

 the hemispheres is extremely convoluted, the gyii being 

 numerous and separated by deep sulci. There is a well- 

 marked SyMan fissure, with a central lobe, or insula. A 

 rudiment of a posterior cornu has been observed in the 

 lateral ventricle. The corpus callosum is small, relatively 

 to the size of the hemispheres, and the anterior commissure 

 is almost obsolete. The medulla oblongata has corpora 

 trapezoidea. The oKactory nerves are wanting — a circum- 

 stance which agrees with the entire absence of ethmoidal 

 turbinals. The eye has a thick sclerotic, and there is a 

 choanoid muscle ; no nictitating membrane is present. 



The external auditory aperture is so small as to be easily 

 overlooked. The meatus auditorius is a nan-ow undulating 

 tube about two inches long. The tympanic membrane is con- 

 cave externally ; and, as is usual in the Cetacea, is connected 

 by a ligament with the handle of the malleus. There is 

 only a small aperture in the stapes. The tensor tympani 

 arises, as in Carnivores, from a fossa in the periotic ossifi- 

 cation. 



The Eustachian tube passes through the notch in the 

 pterygoid and opens into the nasal passage on the inner 

 side of that notch. Close to its commencement it com- 

 municates, by an oval aperture, with a remarkable air 

 chamber, which extends backwards between the periotic mass 

 and the basis cranii, and forwards to the under side of the 

 expanded part of the maxilla, where it opens into the canal 

 between the maxilla and the frontal already described. 

 These chambers, like the bronchi, are generally full of 

 nematoid worms. The testes and penis of the male are 

 enormous in proportion to the size of the body. The penis 



