92 THE BONES. 



posterior nasal spine, whicli is altogether rudimentary, or even null in animals ; the orifice of 

 the posterior palatine canal, which belongs entirely to the palate boue; the pterygo-palatine 

 foramen ; lastly, the pterygoid process, which represents tiie pterygoid bone of animals. The 

 vertical portion foims the external wall of the nasal cavities by its internal face, and by its 

 external face concurs in the formation of the zygomatic or temporal fossa. 



9. Malar bone. — This oflfers three faces. The external, or cutaneous, serves as a base for the 

 most salient part of the cheek. The superior, or orbital, forms part of the external wall and 

 floor of the orbit ; it belongs to a long apophysis — the orbital process — which rests on the 

 sphenoid and frontal bones. The posterior face is smooth and concave behind, where it aids to 

 form the temporal fossa; in front it is uneven, and articulates with the supermaxilla. The 

 posterior, or masseteric border, unites with the zygomatic process of the temporal bone. 



10. Lachrymal bone. — This bone is also called the os unguis in Man, because of its likeness 

 to the nail in shape and tenuity. It is entirely lodged in the orbit, and its external face is 

 divided into two portions by a vertical crest ; the portion situated in front of this crest forms 

 part of the lachrymal groove. By its internal face, the lachrymal bone limits, outwardly, 

 the bottom of the nasal cavities, and covers the anterior cells of the ethmoid ; by its posterior 

 border, within the orbit, it articulates with the os planum of the ethmoid. 



11. Nasal bone. — The proper bones of the nose of Man exhibit a great analogy to those of 

 the Dog. Tliey do not possess a nasal prolongation, and they articulate with the lateral 

 cartilage of the nose. 



12. Vomer. — The same general form and relations as in Solipeds. 



13. Inferior maxillary bone. — This bone in Man is in shape somewhat like a horse-shoe. It 

 is nearly of the same witlth throughout its whole extent. The symphysis is vertical — a 

 character peculiar to Man. Below this symphysis is a triangular projection — the mental 

 eminence. The genial surface of the Horse is replaced by four little tubercles, termed the 

 genial processes. The alveoli of the molar teeth form a great projection on the inner face of 

 the bi)ne. The mylo-hyoid ridge is very developed. The superior orifice of the dental canal 

 is covered by a little sharp lamina. From this oritice begins the mylo-hyoidean groove. The 

 coronoid process is short ; the condyle is bent towards the median line, and the sigmoid notch 

 is wide and shallow. The superior border contains fourteen or sixteen alveoli. 



Aeticle III. — The Thorax. 



The thorax represents a coinoid cage, elongated from before to behind, 

 suspended under the vertebrae of the dorsal region, and contains the principal 

 organs of respiration and circulation. It is composed of bony arches named 

 ribs, thirty-six in number — eighteen on each side — and a single piece — the 

 sternum, which serves for the direct or indirect support of the inferior extremi- 

 ties of the ribs. 



The Bones of the Thorax in particular. 

 1. Sternum of the Horse (H^jial Spine) (Fig. 56). 



This is an osteo-cartilaginous body, elongated from before backwards, 

 flattened on each side in two-thirds of its anterior extent, and above and below 

 in its posterior third ; it is slightly curved on itself, and situated beneath the 

 thorax in an oblique direction downwards and backwards. It offers for study, a 

 superior face, two lateral faces, three borders, and two extremities. 



Faces. — The superior face, shghtly concave longitudinally, represents an 

 isoscelated lengthened triangle, the summit of which is directed forwards ; it 

 constitutes the floor of the thoracic cavity. The inferior face is shaped like the 

 keel of a ship, having in its middle a longitudinal ridge, which decreases in 

 height from before to behind. It has two inclined planes placed towards each 

 other, each of which has two parts — a superior and an inferior. The first shows 

 eight diarthrodial cavities, which receive the inferior extremity of the cartilages of 

 the true ribs. These cavities are elongated vertically, and draw closer to each other 



