424 THE ANATOMY OF VEETEBKATED ANIMALS. 



2. The TnchechidcB, or Walmses, are devoid of external 

 ears, but resemble the Otaridce in their mode of standing 

 and walking. The skull resembles that of the Bear in the 

 same respects, biit the muzzle is distorted by the enormous 

 development of the superior canines. The Walruses re- 

 semble the Bears in another point, namely, in the pre- 

 sence of a sup2^1ementary bronchus ; the right bronchus, 

 before it reaches the lung, dividing into two trunks, a large 

 and a small. The thyroid cartilage is deeply excavated, in 

 front, by a triangular fissure ; and the epiglottis is extremely 

 small. 



In the brain, the remarkably large and richly convoluted 

 hemispheres cover the cerebellum, and present a mdi- 

 mentary posterior cornu. The anterior commissure is very 

 small, as are the oKactoiy nerves. 



The dentition of the Walrus is extremely peculiar. In 

 the adult, there is one simple conical tooth in the outer 

 pari of the premaxiUa, followed by a huge tusk-like canine, 

 and three, short, simj^le-f anged, teeth. Sometimes, two other 

 teeth, which soon f aU out, lie behind these, on each side of 

 the upper jaw. In the mandible there are no incisors, but 

 a single short canine is followed by three, similar, simple 

 teeth, and by one other, which is caducous. 



The dental formula is therefore i. -— - c. r^ p.m.m. ~' 



3. The PhocidcB, or ordinary Seals. — The pinna is alto- 

 gether absent. The hind limbs are permanently stretched- 

 out, parallel with the tail ; and, consequently, they are unable 

 to support the body, or assist in locomotion on land. 



The space between the orbits is extremely naiTOw, and 

 supra-orbital processes are absent. The bulla tympani is 

 very large and thick- walled ; and the middle, are much 

 shorter than the outer, digits of the pes. 



The common Seal {Phoca vitulina) is a native and acces- 

 sible member of this group. It has a rounded head and 

 a neck which is well marked, though shorter in proportion 

 than that of the Eared-seals. The nasal apertures are slit- 



