xi. 
tooth on either side of each jaw, which is the predecessor of the 
third and last pre-molar. Only in the Anteaters (Myrmeco- 
phagide ), the Pangolins (Manidw), and the Echidna, are teeth 
entirely absent at al/ stages of growth. 
SKELETON. 
Skeleton.—The skeleton may be briefly defined as that portion 
- of the body of vertebrate animals which forms the framework on 
which the muscles are supported. In the adult state the 
greater part of this framework consists of osseous tissue, or bone, 
the remainder being cartilage. Bone is mainly built up on a 
gelatinous basis, strongly impregnated with salts of lime, chiefly 
phosphate. After the teeth, the bones are the most imperishable 
of al] the organs of the body, and are, therefore, of great value in 
affording reliable means of affixing the aftinities of extinct with 
recent forms. The skeleton is divided into two parts, the axial, 
consisting of the skull and vertebral column, and the appendicular, 
pertaining to the limbs. 
Skull.—In the skull, or cranium, of adult Mammals, all the 
bones, with the exceptions of the lower jaw, the auditory ossicles, 
and the bones of the hyoid arch, are immovably articulated 
together. The cranium, thus formed of numerous originally 
independent ossifications, consists of a brain-case for the enclosure 
and protection of that organ, and a face for the support of the 
organs of sight, smell, taste, mastication, defence, and offence. 
The brain-case articulates directly with the first cervical vertebra 
by means of a pair of oval prominences, called condyles, placed on 
each side of the large median foramen, which transmits the spinal 
cord; this method of articulation is termed dicondylian, and is 
only present in one other class of Vertebrate Animals, the 
BaTrRACcHIA, and this, together with several other characters, com- 
mon to these classes only, has given authority to the apparently 
well-founded assertion of the remote common origin of the Mam- 
malian and Batrachian types. 
Vertebre.—The vertebral column consists of a series of distinct 
bones, called “vertebre,” arranged in close connection with one 
another along the dorsal aspect of the body in the median line, and 
extending from the posterior margin of the cranium (to which it 
is firmly articulated) to the tip of the tail. The number of distinct 
bones varies greatly, principally owing to the elongation, or other- 
wise, of that appendage. In the mammalian vertebre the ends 
of the centra are usually flattened, but in the cervical region of 
some UncuxatTa certain of the vertebre may be opisthoccelous, 
that is having the hinder surface concave. The vertebral column 
is for convenience divided into five regions, cervical, dorsal, 
lumbar, sacral, and caudal. 
Cervical.—The cervical region forms the anterior portion of 
the column, and its first vertebra, called the atlas, articulates 
