64 OSTEOLOGICAL GALLERY. 



bones, the turbinal bones (f), and forming the narial or olfactory 

 chamber. Below this chamber, and forming in part its floor and 

 walls, is the jaw, composed of the maxillary and premaxillary bones 

 (mx and pmx), in which are implanted the upper teeth, the lower 

 ones being similarly fixed along the upper edge of the mandible. 

 In an upper view of the skull the component parts of its roof are 

 seen as paired bones placed one in front of the other along the 

 middle line. Of these the hindmost are the parietals (pa), pre- 

 ceded by the frontals (fr), and by the small and narrow nasal 

 bones (no), placed between the upper edges of the maxillary bone 

 where it rises to form the side-walls of the olfactory chamber. 

 External to these bones are the zygomatic arches (fig. 26, zy), which 

 serve to support and protect the masticatory muscles, and which 

 are more or less developed in direct proportion to the biting-power 

 of their owners. The hindmost part of the skull is made up of 

 the supraoccipital (so), a pair of exoccipitals (exo), and the basi- 

 occipital (bo), surrounding the large opening through which the 

 spinal cord passes the foramen magnum. 



The mandible consists simply of a pair of solid bones, joined 

 together in front where they form the chin, but widely separate 

 behind, each with a high projecting branch, the coronoid process 

 (cjo), for the attachment of the jaw-muscles, and an articular pro- 

 cess, the condyle (cd), which forms part of the hinge on which the 

 mandible works. This hinge is generally transverse to the general 

 axis of the skull ; but in some Orders, such as the Rodents, the 

 condyle is lengthened antero-posteriorly, and works in a correspond- 

 ing longitudinal depression in the base of the skull. 



The hyoid apparatus (h) consists of a series of small bones 

 suspended from the posterior part of the cranium, and supporting 

 the larynx and root of the tongue. 



The dentition of Mammals is of two kinds. In some few forms, 

 known as " homodont," all the teeth are of one type or pattern 

 as in the Sloths, Armadilloes, Dolphins, &c. ; the remainder, or 

 " heterodont " Mammals, which form the great majority, are pro- 

 vided with teeth of several different types. Thus in the Dog's skull 

 (fig. 27) the three small teeth fixed on each side in the premaxilla 

 (pmx) are the incisors, or cutting-teeth (2) ; next follows a long and 

 powerful tooth, known as the canine (c). Behind this there are 



