THE BONES. 63 



Structure : compact bony tissue, but porous ; many canals for 

 nerves and veins. 



Development: one ossific nucleus in the centre, about the 5th 

 month after birth. 



65. b. Azygos Bones of the Face. 



6. Vomer, Ploughshare bone. 



Situation : in the centre of the nasal cavity, forming the poste- 

 rior part of the septum. 



Figure: flat, angular. Portions: 2 surfaces, 4 borders. 



Conjunctions with: Sphenoid, Ethmoid, both Superior Max- 

 illary and Palate bones, and the cartilage of the nasal septum. 



1. Surfaces, with small grooves for vessels and nerves, covered with mucous 

 membrane. 



2. Borders : a. Superior, mar go sphenoidalis, short, thick, with a deep groove 

 and two lips, alte vomeris, for the reception of the rostrum sphenoidale. 



b. Inferior, palatinus, maxillary, the longest, unites with die crista nasalis of 

 Sup. Maxillary and Palate bones. 



c. Anterior, m. ethmoidulis, unites with the lamina perpendic. of the Ethmoid, 

 below with the cartilage. 



d. Posterior, m. gutturalis, free, thin, sharp, inclining from above and be- 

 hind to below and before, separates the posterior openings of the nasal cavity, 

 choana. 



Structure : the Vomer consists of 2 very thin plates of compact 

 bone, the upper separated more than the lower. 



Development: begins below, with the 3d month of foetal life, 

 and is only completed in the 12th year. Ossification proceeds 

 from without inwards, so that for a long time a groove exists 

 between both plates for the reception of the Sphenoid and Ethmoid 

 bones. 



66. 7. Maxilla inferior, Mandibula, Inferior, lower 

 or under jaw. 



Situation : at the inferior region of the face. 

 Shape : of a horse-shoe, parabolic. 



Portions: a central horizontal body; 2 lateral vertical ascend- 

 ing rami. 



Conjunction: with the temporal bones. 



1. Body, curved like an arch, consists originally of two pieces of bone 

 which unite anteriorly in the central line, to form an arch, the chin, mentum, 

 ytvuov. 



NOTE. In many animals a suture exists in this place ; in Serpents a move- 

 able articulation. The chin of animals never forms an arch, but always an 



