Transcribe Illustrated descriptive catalogue of school series of skeletons (1881)

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SCHOOL SERIES OF SKELETONS.                                                7

jaw is formed of a single bone, and articulates directly with the 
cranium, and not by the interposition of another bone. Moreover, 
the bodies of the vertebra are formed of three pieces, one large 
and sub0cylindrical, termed the centrum, capped on either end by 
a thin disk-like piece termed an epiphysis. *

All mammals, save Sirenia and Cetacea, have two pairs of limbs, 
and never more. When, as in the above mentioned orders, but one 
pair is present, it is invariably the forward pair.

Mammals are most often clothed with hair, but they may be encased 
in an armor of bony plates, like the Armadillos; protected by 
overlapping horny scales, like the Pangolins; or even covered with
a naked, smooth skin, as are the Whales (Cetacea). 
The skull is an extremely complex structure, being composed 
of forty-five bones, not including the auditory ossicles. According 
to Oken these represent three highly modified vertebrae, besides the 
bones of the face, auditory and nasal regions. According to Owen, 
four vertebrae are represented.

A noteworthy characteristic of the Mammalia is the almost constant 
number, seven or cervical vertebrae. The long neck of the 
Giraffe and the short one of the Porpoise have the same number. 
The only exceptions are Hoffman's Sloth and the Manatee, which
have but six, and the Three-Toed Sloths, which have nine. The 
dorsal vertebrae support the ribs, and vary from nine in Hyperoodon
to twenty-four in the Two-Toed Sloth, the average number 
being thirteen or fourteen. This number is less than in most reptiles, 
and greater than in any bird.

All of the ribs articulate with the vertebrae, and the anterior
ones with the sternum. + But one rib may join the sternum, as in 
some whales, or as many as ten, this number occurring in the 
Common Seal (Phoca vitulina).

The lumbar vertebrae bear no ribs, and are usually distinguished
by long transverse processes. The sacrals are those to 
which the pelvis is joined.

____

* The Monotremata have no epiphyses, and in the Sirenia they appear very 
late in life if at all.

+ In the Cetacea, the last rib is usually suspended by ligaments at some 
distance from the vertebrae.

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                  SCHOOL SERIES OF SKELETONS.                                                7

jaw is formed of a single bone, and articulates directly with the cranium, and not by the interposition of another bone. Moreover, the bodies of the vertebra are formed of three pieces, one large and sub0cylindrical, termed the centrum, capped on either end by a thin disk-like piece termed an epiphysis. *

All mammals, save Sirenia and Cetacea, have two pairs of limbs, and never more. When, as in the above mentioned orders, but one pair is present, it is invariably the forward pair.

Mammals are most often clothed with hair, but they may be encased in an armor of bony plates, like the Armadillos; protected by overlapping horny scales, like the Pangolins; or even covered with a naked, smooth skin, as are the Whales (Cetacea). The skull is an extremely complex structure, being composed of forty-five bones, not including the auditory ossicles. According to Oken these represent three highly modified vertebrae, besides the bones of the face, auditory and nasal regions. According to Owen, four vertebrae are represented.

A noteworthy characteristic of the Mammalia is the almost constant number, seven or cervical vertebrae. The long neck of the Giraffe and the short one of the Porpoise have the same number. The only exceptions are Hoffman's Sloth and the Manatee, which have but six, and the Three-Toed Sloths, which have nine. The dorsal vertebrae support the ribs, and vary from nine in Hyperoodon to twenty-four in the Two-Toed Sloth, the average number being thirteen or fourteen. This number is less than in most reptiles, and greater than in any bird.

All of the ribs articulate with the vertebrae, and the anterior ones with the sternum. + But one rib may join the sternum, as in some whales, or as many as ten, this number occurring in the Common Seal (Phoca vitulina).

The lumbar vertebrae bear no ribs, and are usually distinguished by long transverse processes. The sacrals are those to which the pelvis is joined.

____

The Monotremata have no epiphyses, and in the Sirenia they appear very

late in life if at all.

+ In the Cetacea, the last rib is usually suspended by ligaments at some distance from the vertebrae.