TEE HEAD. 69 



4. Pterygoid Boxe (Figs. 34, 38).^ 



A small and very short bone, elongated from above to below, flattened on 

 both sides, and situated on the inner aspect of the subsphenoidal process, but 

 external to the vomer. 



Its external face is in contact with the palate and sphenoid bones ; the 

 internal is smooth, and covered by the pharyngeal mucous membrane. Its 

 superior extremity is tapering, and concurs in forming the Vidian canal ; the 

 inferior is thickened into a small pointed process (the hamular process), the 

 apex of which, directed backwards, offers outwardly a groove which serves as a 

 pulley to the tendon of the tensor palati muscle. 



This bone is composed entirely of compact tissue, and is developed from a 

 single centre of ossification. 



Differential Characters in the Pterygoid Bone of other Animals. 



A. Ox, Sheep, Goat. — The pterygoid of the Ox, Sheep, and Goat is very wide, and closes 

 an aperture left between the sphenoid and palatine bones. 



B. Camel.— In the Camel the pterygoid is short, broad, and applied to tiie internal face 

 of the subsphenoidal process and palatine crest. It does not concur in tlie formation of the 

 Vidian canal. Its inferior extremity has a narrow and deep fissure. 



C. Pig. — (See the description of the palatine bone.) 



D. Camivora. — This bone is very strong in Carnivora, and quadrilateral in shape. 



5. Malar or Zygomatic Bone (Figs. 26, 34). 



This bone, also designated the ju^cd bone, is elongated from above 

 to below, flattened on both sides, and irregularly triangular in shape ; it is 

 situated on the side of the face, and articulates with the supermaxillary, 

 lachrymal, and temporal boues. It is described as having two faces, two borders, 

 a base, and a summit. 



Faces. — The external face comprises two portions separated from each other 

 by a semicircular ridge that extends from the summit to the middle of the 

 anterior border of the bone, and concurs to form the outer margin of the orbit. 

 The anterior portion, smooth and concave, belongs to the orbital cavity. The 

 posterior, more extensive, is also smooth and slightly convex. The internal face 

 is excavated in its central part, which corresponds to the maxillary sinus. On 

 its margin it shows denticulations and lamellte for articulation with the super- 

 maxillary bone. 



Borders. — The anterior, thin and denticulated, is joined to the lachrymal 

 bone. The posterior, or masseteric border, is thicker, and constitutes a roughened 

 crest, the zygomatic ridge, which is continued above with the posterior border of 

 the process of the same name, and below with the maxillary spine. 



Base and summit. — The base, very thin, is united to the supermaxillary bone. 

 The sunomit, flattened from before to behind and bevelled on its anterior face, 

 joins the zygomatic process, and forms with it the jagal bridge, or zygomatic arch. 



Structure and deveJofmeni. — This bone is rather spongy in its upper part, and 

 is developed from a single nucleus of ossification. 



Differential Characters in the Malar Bone of otheu Animals. 



A. Ox, Sheep, Goat. — The malar bone of Ruminants is very developed. The zygomatic 

 crest is no longer formed by the posterior border of the bone, but is carried to the posterior 

 part of the external face, and runs parallel with the eyebrow. The summit is bifurcated, the 



This bone is the representative of the internal icing of the pterygoid process in Man. 



