420 THE ANATOMY OF VERTEBRATED ANIMALS. 



tlie anterior ones, and form a sort of heel to the blade-like 

 anterior portion of the crown. An oblique ridge connects 

 the outer and larger of the two posterior cusps with the 

 small inner and anterior cusp. The second molar has a 

 broad quadricuspidate crown, the inner posterior cusp being 

 almost obsolete. The crown of the last 'molar is small, 

 simple, and obtusely conical. 



It thus appears that the sectorial, or carnassial, teeth in the 

 two jaws differ in their nature, the upper being the last pre- 

 molai-, and the lower the anterior molar. The milk dentition 



of the Dog is d.i. ^ d.c. ^ d.m. ^' the " first premolar" 



of the adidt dentition having no deciduous predecessor ; so 

 that, in this, as in so many other cases, it is doubtful whether 

 it ought to be counted in the milk, or in the adult, denti- 

 tion. The middle deciduous molar in both jaws resembles 

 the hindermost premolar of the adult dentition, and the 

 hindermost, the first molar of the adult. The so-called "first 

 premolar " of the adult, and the anterior molars, appear 

 before any of the deciduous molars are shed. 



The coecum of the Dog is long, and folded upon itself, in 

 which respects it is unlike that of other Carnivores. The 

 arch of the aorta gives off an anonyma and a left sub- 

 clavian. 



In the brain, the olivary bodies are inconspicuous, the 

 corpora trapezoidea large, and the corpora mammillaria 

 distinctly double. The oKactory lobes are very large, and 

 expand posteriorly on the sides of the brain into a broad 

 mass continuous with the gyrus uncinatus, or hippocampal 

 lobule. The cerebral hemispheres extend for a considerable 

 distance over the cerebellum, in the upper view, and overlap 

 it laterally. The Sylvian fisstire does not extend more 

 than haK-way to the median fissure. The surface which 

 answers to the msM?a is quite smooth. The. anterior ends j 

 of the calloso-marginal sulci pass on the upper surfaces j 

 of the hemispheres, and give rise to the " crucial " sulcus. 

 There are three principal gyri upon the outer surfaces of j 

 the hemispheres ; one which immediately bounds the Sylvian j 



