THE DENTITION OF THE BOG. 357 



but tlie posterior lobe is small in the fourth, which differs but 

 little from tlie rest. The first molar, on the other hand, is a 

 large tooth, with a blade-like crown, which bites against the 

 inner side of the upper fourth premolar, and is called the 

 carnassial or sectorial tooth of the lower jaw. The crown is 

 elongated, and presents a large anterior external cusp, divided 

 into two lobes by a deep notch. On the inner side of this is 

 a small internal cusp. The two posterior cusps are very much 

 lower than the 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 cusjd 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 

 premolar, and the lower the anterior molar. The milk denti- 

 tion of the Dog is cl.i. ^^^ d.c. J^i <^^-^^' ^"^15 the " first premolar" 



of the adult 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 iu the adult, dentition. 

 The middle deciduous molar in both jaws resembles the hinder- 

 most 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 decid- 

 uous molars are shed. 



The caecum 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 anonjmia and a left subclavian. 



In the brain, the olivary bodies are inconspicuous, the 

 corpora trapezoidea large, and the corpora mammillaria dis- 

 tinctly double. The olfactory lobes are very large, and ex- 

 pand 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 later- 

 ally. The Sylvian fissure does not extend more than half-way 

 to the median fissure. The surface which answers to the 

 insula is quite smooth. The anterior ends of the calloso-mar- 

 ginal sulci pass on the upper surfaces of the hemispheres, and 

 give rise to the " crucial " sulcus. There are three principal 

 gyri upon the outer surfaces of the hemispheres ; one which 



